Release 4.3.1

Changes from 4.3.0 to 4.3.1

This is a maintenance release focused on CTable nested-column ergonomics,
grouped reductions, and API/documentation polish.

CTable nested columns and grouped reductions

• Nested column names in group_by() results: grouped output columns can now
  preserve dotted/nested names such as trip.sec instead of requiring valid
  Python identifiers.
• Column-object selectors: CTable.group_by() and CTable.sort_by() now
  accept Column objects as well as string names, enabling idioms such as
  t.group_by(t.trip.sec) and t.sort_by(t.trip.sec).
• Grouped arg reductions: CTableGroupBy now supports argmin() and
  argmax(), plus agg({"col": "argmin"}) / agg({"col": "argmax"}).
  Results are logical row positions in the grouped table or view; groups with no
  non-null values return -1.

NDArray constructor ergonomics

• blosc2.array(): added a NumPy-like constructor for NDArrays. It mirrors
  blosc2.asarray() but defaults to copy=True, so passing an existing
  NDArray creates a copy unless copy=False or copy=None is requested.

Documentation

• Expanded the CTable reference with RowTransformer, Column.row_transformer,
  and CTableGroupBy.argmin / argmax documentation.
• Added blosc2.ndarray(), blosc2.dictionary(), and related public schema
  factory functions to the Schema Specs reference.
• Moved blosc2.group_reduce() into the Reduction Functions reference and
  updated its example to use Blosc2 NDArrays.