Use `gitoxide` for `get_tags`

[cruessler]

This PR is a draft, currently intended for a discussion with @Byron about the part of the API to be used for getting a reference’s name. I intend to mark it as ready once I’ve figured out how to best use the existing APIs.

Update 2025-06-09: this PR is now ready for review.

This PR changes the following:

• It converts get_tags to use gitoxide under the hood.
• It seems the current implementation might have a bug. At least, the gitoxide version properly show an @ symbol in the tags popup for annotated tags, something the libgit version doesn’t do. (I didn’t investigate this in depth, though.)

I followed the checklist:

• [x] I ran make check without errors
• [x] I tested the overall application