Added missing activation checkpointing for DeepseekV4 model

[dipakg-lang]

Description

Added missing activation checkpointing for DeepseekV4 model

The rest of the description includes relevant details and context, examples:

• This was missed while doing the model bring up,
• adss missing activation check pointing at the missing places,
• We need this for efficient training
• Considering we are working with Deepseek v4 which uses single KV proj we had to introduce a new check point name for it in maxtext

If the change fixes a bug or a Github issue, please include a link, e.g.,:
FIXES: TDB

Notice 1: Once all tests pass, the "pull ready" label will automatically be assigned.
This label is used for administrative purposes. Please do not add it manually.

Notice 2: For external contributions, our settings currently require an approval from a MaxText maintainer to trigger CI tests.

Tests

Please describe how you tested this change, and include any instructions and/or
commands to reproduce.

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

❌ Patch coverage is 68.18182% with 7 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/maxtext/layers/nnx_decoders.py	25.00%	3 Missing ⚠️
src/maxtext/layers/attention_compressed.py	84.61%	2 Missing ⚠️
...axtext/checkpoint_conversion/inspect_checkpoint.py	0.00%	1 Missing ⚠️
src/maxtext/utils/estimator.py	75.00%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!