v0.22.0 — layout and stats

Minor bump: layout and stats (upstream batch 2). Default output stays
byte-identical except for the deliberate changes under "Changed", each
guarded by tests/default_output_022.rs.

Added

• render::text::text_width(text, size) and ggplot2's check.overlap
  priority order for axis labels, ported from the consumer's ticks.rs so
  ggplot-rs owns outer-label overflow and overlap thinning centrally.

• Theme.axis_text_x_fit: AxisLabelFit { Clip, Shift, #[default] Reserve }
  and Theme.axis_text_x_check_overlap (default false), with
  GGPlot::axis_text_x_fit/axis_text_x_check_overlap builders.

• GuideLegend.byrow/max_rows, with with_byrow/with_max_rows
  builders: an explicit nrow/ncol legend grid (column-major unless
  byrow), and an auto-wrapped horizontal legend that ends in a trailing
  "+N more" when it still doesn't fit max_rows.

• Position::per_panel() (default false) and Position::validate()
  (default no-op); PositionStack/PositionFill are per-panel.

• PositionStack/PositionFill gain a vjust field (default 1, the
  previous top-anchored behaviour) with a with_vjust builder and free
  functions position_stack()/position_fill(), matching ggplot2's
  position_stack(vjust =)/position_fill(vjust =) (#147). vjust != 1
  also writes an ymax column holding the segment's top.

• ScaleSizeContinuous::area(max_size) / GGPlot::scale_size_area(max_size)
  (ggplot2's scale_size_area(), #150): size ∝ √(value) so that area
  (not radius) is proportional to the data, with 0 mapping to 0. NA/non-
  finite input maps to None. A non-finite or non-positive max_size
  warns and falls back to 6.

• geom_boxplot(stat = "identity"): new Lower/Middle/Upper/
  Outliers aesthetics (Aes::lower/middle/upper/outliers, D4
  extensions) let a layer supply the five-number summary directly instead
  of ggplot-rs computing it, matching ggplot2 (#149) — ymin/ymax are
  also required, as in ggplot2 4.0.3. outliers takes a comma list with
  optional brackets ("7, 9" or "[7, 9]"), or a single bare number; an
  unparsable part is skipped with one warning. The boxplot now consumes
  tooltip()/data_attr() (consumes_tooltips is true).

• Geom::mapped_only_columns() (D3, default empty — GeomBoxplot returns
  lower/middle/upper/outliers): a raw column of that name is
  dropped right after resolve_mappings unless the aesthetic was
  actually mapped, so a column that merely happens to share the name
  (e.g. a SQL alias) can't be mistaken for a mapped one, and so a raw
  lower is never drawn as a boxplot hinge. Scoped to GeomBoxplot
  alone — see the Value::Na/non-finite drop bullet under "Changed" for
  how an unmapped lower/middle/upper on any other geom is handled
  without removing it from the data (review #158's final check).

• Geom::validate_layer(pre_stat_columns, stat_name) (default no-op):
  stat-dependent validation beyond required_aes. Under
  stat = "identity", geom_boxplot requires lower/middle/upper/
  ymin/ymax to be mapped (a ValidationError otherwise, matching
  ggplot2 4.0.3's own stat_identity boxplot requirement); under the
  default stat, it requires y.

Changed

• Outer x-axis labels that would cross the SVG edge are kept on-canvas by
  default (allowed #1, #2 — AxisLabelFit::Reserve, the new default):
  the panel narrows by just the overflow if Reserve can reserve enough
  margin, and a label whose own tick has scrolled off the canvas is
  dropped rather than drawn off-page. A plot whose outer labels already
  fit is unaffected (tests/axis_label_fit.rs;
  default_output_022's wide_axis case, re-blessed when the Reserve
  formula bug — finding 1 below — was fixed). The total reservation is
  now capped so the panel can never start beyond the canvas or shrink
  past its own minimum width (review #158's second re-review, LOW): a
  single, centred break whose label is wider than the whole canvas falls
  back to Shift's draw-time adjustment for whatever still overflows
  past the cap (tests/axis_label_fit.rs).

• A single horizontal legend that overflows its one-line layout now
  auto-wraps to more rows instead of running off the panel (allowed #3,
  D7); beyond max_rows it ends in a trailing "+N more" with a build
  warning. A legend that already fits on one line is unaffected. A
  vertical ncol legend grid that still overflows the canvas after its
  width is reserved now also gets a build warning (review #158's second
  re-review, LOW; tests/legend_wrap.rs).

• Tooltip-template placeholders for every position column
  (xmin/xmax/xend/ymin/ymax/yend/lower/middle/upper,
  D9 allowed #7) are now formatted through the x/y scale, the same as the
  bare x/y they're derived from — previously they fell back to the
  plain display format, ignoring a custom formatter or a log-transformed
  scale's inverse transform. A tooltip() template that names one of
  these columns on a transformed scale, or with a custom number
  formatter, now shows a different (correct) value.

• geom_boxplot outliers now widen the trained y domain to include every
  outlier value instead of silently leaving it at the whiskers' extent
  (allowed #6; confirmed as a real bug with a failing test before the
  fix landed — see tests/boxplot_identity.rs). A boxplot whose outliers
  fall outside ymin/ymax renders with a taller y axis.

• A faceted position_stack/position_fill now computes per panel
  instead of on the rows pooled across panels before faceting, matching
  ggplot2 (#146). A plot with 2 or more distinct facet panels and a stack/
  fill layer may render differently; one panel (or none) is unaffected.

• geom_text/geom_label now honour a discrete position_dodge, via the
  same XMapper bar/col/point/errorbar/… already use (#148). A plot that
  dodges text/labels on a discrete x axis renders differently; text/
  labels without a dodge are unaffected.

• geom_errorbar's whisker caps shrink by the dodge group count under a
  discrete position_dodge, so caps from adjacent groups no longer
  visually overlap (#151). An un-dodged errorbar is unaffected.

• A Value::Na (e.g. a SQL NULL) in a position column that is never
  legitimately discrete (ymin/ymax/xend/yend/lower/middle/
  upper/…, i.e. every position column except x/y, which may hold
  discrete category values) is now dropped with the standard "removed N
  row(s) containing non-finite values" warning, the same as Float(NaN)
  already was — previously it silently mapped to 0 with no warning
  (review #158 finding 4). This applies to every geom that uses one of
  these columns, not just geom_boxplot: e.g. geom_errorbar/
  geom_pointrange/geom_ribbon with a Value::Na ymin now drop that
  row with a warning instead of silently drawing it from 0 — matching
  ggplot2, which has always dropped a missing aesthetic's row this way.
  The new lower/middle/upper columns also drop a non-numeric,
  non-Na value (a stray string) the same way, since they have no
  legitimate discrete use. A plot whose position data has no Na is
  unaffected.

• lower/middle/upper are excluded from the above Value::Na/non-
  finite drop, the pre-stat y-scale transform, and the y-scale training
  when the layer never mapped the corresponding aesthetic — a raw,
  unmapped column under one of these names (e.g. a forecast's confidence-
  bound columns on a plain geom_line) is otherwise left completely
  untouched in the layer's data, so a tooltip("{lower}") placeholder or
  a facet_wrap("upper") on it still works, exactly as any other
  unmapped column would (review #158's final check — round 3's universal
  drop of these names from the data for every geom was itself a
  regression on both of those). geom_boxplot's own hinges — mapped
  under stat = "identity", or computed fresh by its default stat — are
  unaffected either way.

Breaking

• Theme gains two new public fields, axis_text_x_fit: AxisLabelFit and
  axis_text_x_check_overlap: bool — an external Theme { .. }
  struct-literal pattern without ..Default::default() (or
  ..theme_gray()/another preset) no longer compiles.

• GuideLegend gains two new public fields, byrow: bool and
  max_rows: Option<usize> — same breakage for an external
  GuideLegend { .. } struct literal without ..Default::default().
  Neither struct is #[non_exhaustive].

• guide::axis::draw_x_axis gained a canvas: &Rect parameter (the full
  SVG viewport, not just the panel) — a deviation from the plan, needed
  for the outer-label-fit edge checks (B3-1): an off-canvas label can't
  be detected from the panel rect alone. An external direct caller of
  draw_x_axis needs to pass it (backend.total_area()).

• PositionStack/PositionFill are now structs with a vjust field
  instead of unit structs — an external PositionStack { .. }/
  PositionFill { .. } struct-literal pattern no longer compiles (the
  bare value PositionStack/PositionFill still does, via a const of
  the same name — dodge.rs's existing PositionDodge precedent).

• New Aesthetic variants Lower/Middle/Upper/Outliers: an
  exhaustive external match on Aesthetic no longer compiles.

• Geom::setup_data gained a second parameter,
  warnings: &mut Vec<String> (a deviation from the plan, needed so
  GeomBoxplot::setup_data can warn on an unparsable outlier value
  through the existing warnings channel rather than a new one or
  eprintln!): fn setup_data(&self, data: &mut DataFrame) becomes
  fn setup_data(&self, data: &mut DataFrame, warnings: &mut Vec<String>).
  An external Geom impl overriding it needs the new parameter.

• The arrow feature now pins arrow = "59" (was "53"), still with
  default-features = false. GGPlot::new(batch) and the GGData impl for
  arrow::record_batch::RecordBatch compile unchanged against arrow 59 —
  no source changes were needed in src/data/source.rs. This lets Arrow-
  native producers on arrow 59.x (e.g. the inventory-rs DuckDB/Parquet
  ingest path) hand RecordBatches to ggplot-rs directly, without a copy
  through an intermediate arrow 53 batch (#123). The polars feature is
  unaffected: polars vendors its own polars-arrow crate rather than
  depending on the arrow crate, so the two can be enabled together with a
  single arrow v59.3.1 in the dependency tree. This is a semver-relevant
  change for arrow-feature users: code that names arrow-53-specific types
  (e.g. via arrow = "53" pinned directly) needs to move to arrow 59 too,
  since arrow does not guarantee cross-major type compatibility. Originally
  #143; folded into 0.22.0.