Add tr(KEY) support

[Zero-1729]

For brief context, I have been using this library for work with descriptors in a separate ts-based project, and I noticed it didn't handle parsing single-key taproot descriptors tr(KEY).

This PR adds support for parsing single-key taproot descriptors (i.e., tr(KEY)). I've used the existing p2tr and regex pattern definitions. Happy to make any adjustments to fit the repo code style or any other related changes.

[landabaso]

Hi @Zero-1729,

Thank you so much for this PR! I'm thrilled to see contributors joining in. :)

I'll need a bit of time to review it thoroughly. Have you implemented this as a proof of concept, or is it already functioning well within your project?

From a quick look, I believe we'll need some basic tests. This ensures that the functionality works as intended and helps prevent unintentional breakages in future releases.

[Zero-1729]

@landabaso Thanks for working on the library.

I'Il need a bit of time to review it thoroughly. Have you implemented this as a proof of concept, or is it already
functioning well within your project?

Yes, it works as expected. I use the library to parse descriptors and modify their formats; it returns all the useful bits of the descriptor (e.g., key, key path, fingerprint, etc.) for other helper functions to wrangle and create private or public external and internal versions of a given descriptor.

From a quick look, I believe we'll need some basic tests. This ensures that the functionality works as intended and helps
prevent unintentional breakages in future releases.

Fair point, l'Il include some test cases.