[Draft] fix logprobs + prompt logprobs

[joerunde]

Description

It turns out when prompt_logprobs are enabled, the static batching model runner will crash when calculating logprobs.

This draft has a failing test, should be a simple fix

[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 🚀

[prashantgupta24]

can we add some comments on when we have to use force_engine_shutdown? Also I wonder if we can make it such that it's part of pytest teardown automatically in case someone forgets to add this which would result in the weird addr-in-use error

[maxdebayser]

Yeah, maybe we could make it an auto-use fixture.