Fix macOS installation by dynamically skipping legacy MaxText directory

[igorts-git]

Description

• Enable custom build hook in pyproject.toml.
• Update build_hooks.py to skip src/MaxText on macOS while maintaining legacy support on Linux.
• Add macOS-specific installation guide to docs/install_maxtext.md.
• Add sys_platform == 'linux' statements from PR #3467

FIXES: #3441

Tests

Linux Wheel Parity Test.
To ensure that the generated package for Linux remains exactly the same as before, I ran the following commands on a Linux environment:

# 1. Build the wheel
pip wheel . --no-deps -w dist/
# 2. Verify the contents of the generated wheel
unzip -l dist/maxtext-0.2.1-py3-none-any.whl > /tmp/file_structure.txt

# Manually compared the files before and after this PR to ensure that they are identical.

Checklist

Before submitting this PR, please make sure (put X in square brackets):

• I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run end-to-end tests tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed, including adding new documentation pages to the relevant Table of Contents (toctree directive) as explained in our documentation.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[bvandermoon]

Since you are handling ignoring the src/MaxText files in this PR, does this comment need to be user-facing? Maybe it could just say that only the runner option is supported on MacOS

[igorts-git]

OK, I changed the wording here. PTAL.