Fail gracefully when track is not a supported file format

[keiranking]

Problem

What happens when the current or selected track(s) are not in the MP3/M4P format, and therefore may either not have the expected metadata, or may not be able to write to it?

Solution

Fail gracefully when track is not a supported file format.

[keiranking]

Our Tagging.Outcome structure, tied to a request that returns a Result<Void, Tagger.Error>, provides a lot of cover to fail gracefully. The main remaining question might be if some oversight in business logic would cause a crash. All my files are supported, and the MVP is for personal use. Descoping for now.