Warn when running on the Linen code path

[ecnal-cienet]

Description

Logs a deprecation banner during config validation when a run selects the Linen code path, and notes the upcoming deprecation in the relevant field descriptions.

What it looks like

W0728 23:10:04 types.py:2922] ================================================================================
W0728 23:10:04 types.py:2923] MAXTEXT DEPRECATION NOTICE: you are running on the Linen code path.
W0728 23:10:04 types.py:2924] Selected by: pure_nnx_decoder=False
W0728 23:10:04 types.py:2925] Linen will be deprecated in the near future and removed after that.
W0728 23:10:04 types.py:2926] Plan to migrate to NNX: leave enable_nnx, pure_nnx and pure_nnx_decoder at their default of True.
W0728 23:10:04 types.py:2927] ================================================================================

Testing

case	banner	Selected by:	Log
defaults (NNX)	no	—	log
enable_nnx=false	yes	enable_nnx=False	log
pure_nnx=false	yes	pure_nnx=False	log
pure_nnx_decoder=false	yes	pure_nnx_decoder=False	log
all three off	yes	all three	log

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 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.

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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