✨Add support for local source files

[mossjacob]

This is a very small PR and I'm definitely open to better ways of doing this!

Some use-cases, e.g. debugging, may require local files to be loaded as a source.

As an example, I added to sources_local.yaml the following lines:

Gene:
  ensembl:
    arabidopsis thaliana:
      release-57:
        url: file:///path/to/local/df_arabidopsis thaliana__ensembl__release-57__Gene.parquet

With the change in this PR I can load this local parquet file. There's almost certainly a better way of doing this so please do enlighten me!
Thanks

[sunnyosun]

This looks good! Could you add a small test for it?

[sunnyosun]

Just letting you know that we are working on a better process than modifying the sources_local.yaml, all the files that you curated will be all registered in your lamindb instance and tracked there. We'll update you with the new process once we are there!

[mossjacob]

Will add a test probably on Monday! Thanks for letting me know, sounds great.

[Zethson]

I'm sorry for abusing this PR to ensure that the CI now runs fine on forked PRs but it does now. So with your test on Monday, we can merge this although this design is going to be succeeded in the future.

Thank you very much!

[mossjacob]

Have now added the test! thanks

[Zethson]

Thank you so much! I made a few edits myself to save you a bit of time and get this in more quickly. I hope you don't mind. If you'd rather have me review smaller PRs instead of making changing to them, please let me know!

1. I ran pre-commit. We are using it on all of our repositories and I'd encourage you to use it for your work and all PRs that you make to our repositories. See https://pre-commit.com/
2. We should not hardcode paths like /tmp because they might not be writable on Windows devices or clusters. We are now using tempfile to create temporary test files.

[mossjacob]

No that's perfect, thanks so much for making those improvements. Completely understood re pre-commit and tempfile!