fix: return correct channel urls from MatchSpec.channel.base_url

[cisaacstern]

Description

This PR adds the tests described in #884.

It also provides a (reference) fix in MatchSpec.channel. I say "reference" because I imagine the maintainers may prefer to handle this in some other way (perhaps by pushing the url parsing I've done in Python here to the Rust layer?), in which case I will certainly have no objection to my "fix" being discarded. But I provide it nonetheless to indicate the general shape of a possible solution.

Thanks all! Happy to contribute to this further if I am able.

[wolfv]

Thanks for the fix! It looks pretty good to me, but I am wondering if there might be an easier way. @baszalmstra recently refactored some parts of this so on the Rust side we have distinct types for channels from (relative) Path, URL, or file URL. Maybe we can expose that in a clean way and have a function on the Rust side that returns the right thing.

But you have clearly identified a nice bug!

I'll wait with merging until we hear from Bas.

[baszalmstra]

Hey! Thanks for this fix! I think we should definitely fix this completely on the rust side. Ill give that a try, do you mind if I amend your PR?

[cisaacstern]

do you mind if I amend your PR?

Yes of course please do, however you see fit!

[baszalmstra]

I modified you code slighty, the rust side already returned everything you needed we just had to convert it properly to python. Your tests seem to succeed with these changes. Thanks for adding those!

[cisaacstern]

Amazing, tysm!