[Bugfix][Model] Jamba assertions and no chunked prefill by default for Jamba

[tomeras91]

#6666 enabled chunked prefill by default for long-context (>32K) models. Jamba is such a model, but it doesn't support chunked prefill.

This PR:

1. Doesn't enable chunked prefill by default for Jamba (currently the only model with seqlen agnostic layers)
2. Adds assertions inside Jamba code that make sure it's not used with chunked prefill or prefix caching which are currently not supported

[github-actions]

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🚀

[tomeras91]

/ready

[WoosukKwon]

LGTM! Sorry for introducing the bug to the Jamba model support.