Track lower-case maxtext package in coverage to unblock Codecov

[ecnal-cienet]

Summary

• Add maxtext (lower-case) to [run] source in .coveragerc alongside MaxText (upper-case).

Why

coverage.py uses [run] source to decide which packages to trace. The config previously listed only MaxText, so files imported via the lower-case maxtext package (the NNX-migrated path at src/maxtext/) were never instrumented. Lines covered by real unit tests therefore showed up on Codecov as null rather than hit, pushing patch coverage artificially low.

The existing [paths] aliasing only merges already-collected measurements across filesystems — it does not control what is traced in the first place.

Checklist

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• 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 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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