Make the submission process more robust by caching dependencies

[nvdaes]

Background

Currently, the validation repo is checked out to validate submissions, and dependencies are installed using requirements.txt.
This may be improved by caching dependencies and refreshing the cache when requirements.txt is updated.
For this, the whole validation repo may be checked out, or just the requirements.txt file, in order to check if dependencies should be checked out restoring the cache or installing them again.

[LeonarddeR]

We can consider moving this to uv as well, since the uv action has proper cache.

[nvdaes]

@LeonarddeR , I don't have experience with uv. I can try to work on it with Uv, but likely my work won't be optimal.

[nvdaes]

I'm working with uv locally, converting to projects addon-datastore-validation and addon-datastore-transforms in my fork.
Please let me know if you think that I shouldn't follow this way @seanbudd @SaschaCowley

[seanbudd]

@nvdaes - converting the repos to uv would be nice. I think they need to be linux/windows agnostic possibly