Release 4.4.3

Changes from 4.4.2 to 4.4.3

This is a maintenance release focused on faster CTable cold-start, printing
and groupby performance, a lighter import blosc2, new raw-storage access
for columns, and support for the new J2K/HTJ2K codec plugins.

CTable performance

• Lazy column opening in views: select() (and other view-producing
  operations) no longer open every projected column up front. A column is
  only opened from storage when the view actually reads it, so selecting and
  then touching a subset of columns — or aggregating a single one — skips
  the cold-start cost of the rest.
• Lazy index opening in queries: query planning no longer opens every
  SUMMARY-indexed column on a wide persistent table; only indexes for
  columns actually referenced by the predicate are loaded.
• Faster table printing: repr()/to_string() now memoise per-column
  sparse gathers for the duration of a render and combine the head and tail
  rows into a single sparse read per column. Each column is read from
  storage once instead of ~6 times (precision detection, width sizing and
  row rendering all hit the cache).
• Groupby with integral float keys: float key columns whose values are
  integral and fit a compact non-negative range (e.g. float32 id/second
  columns) now take the dense single-key fast path instead of the markedly
  slower generic float-hash path. Fractional or non-finite keys fall back
  automatically.
• No tempdir in read mode: opening a .b2z/.b2d store in 'r' mode
  no longer creates a temporary working directory, since nothing is ever
  written.

Lighter imports and prefetcher rework

• asyncio dependency dropped: the on-disk chunk prefetcher used by the
  UDF and numexpr fallback engines now uses plain concurrent.futures
  instead of an asyncio event loop. import blosc2 no longer pulls in
  ~30 asyncio modules, saving ~3 MB of memory footprint at import time.
• Prefetcher deadlock fixed: an exception during evaluation could leave
  the generator finalizer blocked forever in thread.join() while the
  reader thread was stuck on a full prefetch queue. A stop event now makes
  the producer bail out when its consumer goes away.

New features

• Column.raw accessor: returns the underlying storage container of a
  column (NDArray, ListArray, DictionaryColumn, …) directly. Unlike
  Column.__getitem__, which always materializes NumPy arrays, this is the
  column as a blosc2-native compressed object — usable as a lazy-expression
  operand without decompressing, and exposing storage details like schunk,
  chunks or cparams. Note that this is a physical view: fixed-width
  containers are over-allocated to chunk capacity, so slice to len(table)
  to get just the live rows, and no validity-mask or null-sentinel
  processing is applied. Raises AttributeError for computed columns,
  which have no backing storage.
• J2K and HTJ2K codec IDs: blosc2.Codec.J2K and blosc2.Codec.HTJ2K
  expose the IDs for the new JPEG 2000 codec plugins (installable with
  pip install blosc2-j2k and pip install blosc2-htj2k).

Fixes

• --float-trunc-prec and nested columns: the precision-truncation
  filter of the parquet_to_blosc2 CLI now propagates to float fields
  inside nested (struct/list) columns too.
• Guard for unsupported computed-column expressions: expressions that
  would serialize to an empty or non-round-trippable string are now rejected
  with an early, actionable ValueError at add_computed_column() time,
  instead of silently breaking on reload.

Build

• C-Blosc2 updated to 3.1.3.