Make CI faster and more reliable

[konstin]

Currently, github actions take 30min for a single PR CI run (https://github.com/PyO3/maturin/actions/runs/10497103635/job/29079188923?pr=2186), before being added to the merge queue which takes even longer. Between those, there are frequent non-deterministic failures. This is not viable for development, and in general very long for a project of uv's size.

We should implement changes that improve PR turnover time, such as:

• Removing the merge queue for regular merging
• Splitting up test jobs into smaller, independent units
• Improving maturin compile times
• Speeding up slow tests
• Removing unnecessary steps in the test actions