Switch to Narwhals' v2 namespace

[stanmart]

glum will soon pass narwhals.stable.v2.DataFrame`s to tabmat, so we will have to handle them properly. The fact that

isinstance(
    narwhals.stable.v2.Enum([]),
    narwhals.stable.v1.Enum
) == False

would cause issues in from_df, which this update solves.

Note, that

isinstance(
    narwhals.stable.v1.Enum(),
    narwhals.stable.v2.Enum
) == True

so this change does not break the ability to accept v1 dataframes.

Checklist

• Added a CHANGELOG.rst entry

[Copilot]

Pull Request Overview

This PR updates tabmat to use Narwhals' v2 stable namespace (narwhals.stable.v2) instead of v1. This change is necessary because glum will soon pass v2 DataFrames to tabmat, and v1 type checking is incompatible with v2 objects. The update also includes parameter name changes to align with v2 API (strict=False → pass_through=True). Since v2 is backwards compatible with v1 objects, this change maintains support for v1 DataFrames.

Key changes:

• Updated all imports from narwhals.stable.v1 to narwhals.stable.v2
• Changed API parameters from strict=False to pass_through=True in accordance with v2 API
• Updated dependency requirements to narwhals>=2.0.0

Reviewed Changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/test_categorical_matrix.py	Updated import to use v2 namespace
src/tabmat/constructor.py	Updated import to use v2 namespace
src/tabmat/categorical_matrix.py	Updated import to v2 namespace and migrated parameter names to v2 API
pixi.toml	Updated narwhals dependency constraint to >=2.0.0 and 2.0.* for oldies environment
pixi.lock	Updated narwhals package version from 1.4.1 to 2.0.1
conda.recipe/meta.yaml	Updated narwhals dependency constraint to >=2

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