Add kv_cache_specs for mistral models

[rzbhatti]

Description

This PR adds kv_cache_specs for mistral modals

Related Issues

Fixes #567

[github-actions]

👋 Hi! Thank you for contributing to vLLM support on Spyre.
Just a reminder: Make sure that your code passes all the linting checks, otherwise your PR won't be able to be merged. To do so, first install the linting requirements, then run format.sh and commit the changes. This can be done with uv directly:

uv sync --frozen --group lint --active --inexact

Or this can be done with pip:

uv pip compile --group lint > requirements-lint.txt
pip install -r requirements-lint.txt
bash format.sh

Now you are good to go 🚀

[tjohnson31415]

The code is checking for attributes from the FMS config, but the model.config here is the Transformers config class.

Also, we should avoid hard-coded numbers for defaults here if we can.