[Deepseek V4] Add caching support and verify decoding

[Rohan-Bierneni]

Description

PR add caching support to attention_compressed.py and verifies v4 has decoding support with the maxengine/jetstream backend

If the change fixes a bug or a Github issue, please include a link, e.g.,:
FIXES: b/123456

Tests

Decode.py should pass (In progress)

cmd:
output:

Checklist

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