Make CI even faster?

[Wauplin]

Follow-up issue after #2059 cc @bmuskalla

Would be worth trying:

• install dependencies with uv instead of pip Use uv in CI to speed-up requirements install #2072
• cache dependencies between reruns (with 24h retention?)
• split Windows CI to complete even quicker?
• or: regroup tests to avoid complexity (e.g. stop doing repo / not repo and / torch tests separately)

Each item can be taken separately.

[Wauplin]

let's keep it as it is