Add tests for dummy requests creation and removal

[gmarinho2]

Description

Add tests to check if dummy requests are created when there is only one sequence prompt scheduled and removed when a second true request is received.

Related Issues

#204

[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 🚀

[yannicks1]

Hi @gmarinho2, this PR does not look ready yet, do you mind to convert it to a draft while still working on it. Otherwise code owners get notifications to review...