Restrict MacOS symbol exports to the Python module init

[G-D-Petrov]

Reference Issues/PRs

What does this implement or fix?

ld64 on MacOS lacks --exclude-libs,ALL, which leads to symbols from statically linked libraries"leaking" in our wheel.
This PR makes sure that exports are restricted to the module init symbol to stop dyld weak-coalescing of statically-linked deps (e.g. pyarrow's bundled AWS SDK in libarrow) from aborting in aws_fatal_assert.

Any other comments?

Checklist

Checklist for code changes...

• Have you updated the relevant docstrings, documentation and copyright notice?
• Is this contribution tested against all ArcticDB's features?
• Do all exceptions introduced raise appropriate error messages?
• Are API changes highlighted in the PR description?
• Is the PR labelled as enhancement or bug so it appears in autogenerated release notes?

[claude]

ArcticDB Code Review Summary

Build-only change restricting the macOS extension's exported symbols to _PyInit_arcticdb_ext, with packaging and runtime regression tests. The change is sound: the symbol name correctly accounts for the macOS leading-underscore ABI, the export restriction only fires on the non-conda (wheel) AppleClang path where HIDE_LINKED_SYMBOLS is ON, which exactly matches the MACOS_WHEEL_BUILD test skip guard, and pybind's default-visibility PyInit survives the restriction. Both a nm-based packaging check and a pyarrow-before-arcticdb runtime regression are included.

The latest commits add unrelated test/CI cleanups: pinning the conda Windows runner to windows-2022, introducing an unparametrized latest_venv session fixture (used by test_comp_venv_loading_path), and removing stray trailing commas in two @pytest.mark.parametrize argname strings. All are benign — no correctness, safety, or behavioral impact.

PR Title and Description

• Description is empty (template only). Per the review guidelines the description should explain what changed and why — here, that ld64 lacks --exclude-libs,ALL, so exports are restricted to the module init symbol to stop dyld weak-coalescing of statically-linked deps (e.g. pyarrow's bundled AWS SDK in libarrow) from aborting in aws_fatal_assert. The context already lives in the code comments and test docstrings; please lift a sentence or two into the description.

No correctness, memory-safety, API, on-disk-format, or build-configuration issues found. Labels (no-release-notes, patch) are appropriate for a build/test-only change.