Combined slider for slicer plots

[nvaytet]

This adds a new slider for the slicer plot which combines a range slider (two handles) and a single slider (one handle) where the mode can be toggled with a button click.

It also adds text fields instead of a read-only text as readouts, which enables the user to enter the values they want.
If the requested value is outside the range, it will clamp to the bounds of the axes.
If the requested value does not match an exact coordinate value it will snap to the closest value available.

The combined slider is now enabled by default in the slicer plot.

Example:

%matplotlib widget
import plopp as pp
from plopp.data.examples import clusters3d

da = clusters3d(nclusters=50, seed=12).hist(z=100, y=100, x=100)
pp.slicer(da, keep=['x', 'y'], logc=True, mode="combined")

The text boxes also properly handle bin edges and datetime coords (this is why the changes here got quite complicated).

[Copilot]

Pull request overview

This PR adds a new "combined" slider mode to the slicer plot that allows users to toggle between a range slider (two handles) and a single-handle slider within the same widget. It also replaces the read-only label readouts with editable text fields, enabling users to type exact coordinate values directly. The combined mode is enabled by default.

Changes:

• Replaces slice.py with slicing.py, introducing CombinedSliceWidget, BoundedText, BoundedBinEdgeText, and related bounded-text readout widgets
• Extends Slicer and slicer() to support mode ('single', 'range', 'combined') and operation parameters; adds _maybe_reduce_dim for reducing sliced dims; the figure now uses reduce_nodes instead of slice_nodes
• Expands the test suite with parametrized tests for all three modes, including datetime and bin-edge coordinate cases

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/plopp/widgets/slicing.py	New widget file implementing bounded text readouts and combined slider
src/plopp/widgets/__init__.pyi	Exports CombinedSliceWidget from the new module
src/plopp/plotting/slicer.py	Adds mode/operation params, _maybe_reduce_dim, switches figure to reduce_nodes
src/plopp/plotting/superplot.py	Explicitly sets mode='single' for superplot
tests/widgets/slice_test.py	Updated/extended tests for new bounded text readouts
tests/plotting/slicer_test.py	New parametrized tests for all three slider modes
docs/plotting/slicer-plot.ipynb	Updated example notebook to use new combined default and mode='single' for player
docs/getting-started/numpy-pandas-xarray.ipynb	Minor datetime formatting note added
docs/_static/plotting/slicer-plot.png	Updated screenshot

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