Make UUID path parameter conversion more flexible

[edthrn]

Summary

Based on @adriangb suggestion made in this discussion thread, here is a more flexible conversion of UUID path parameters.

UUID representation may vary depending on the system from which it is generated. Some systems may return an hex representation with no hyphens, while some others use upper-case letters.

From Python perspective, they are all valid:

Not handling those cases may yield to hard-to-debug 404 errors.

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.

[adriangb]

looks good to me :)

[Kludex]

This is fine. 🙏

Just a minor nitpick, as I think our test suite focus a lot on readability.