Switch to thiserror or similar

[expede]

NB: Feature requests will only be considered if they solve a pain or present a useful refactoring of the code.

Summary

Problem

rs-ucan today doesn't provide descriptive errors

Impact

It's hard to debug when integrating rs-ucan into applicatons, and makes it difficult to provide good error messages to users.

Solution

Switch from anyhow to thiserror or similar. The general guidance ([even metioned in the anyhow README) is that anyhow is great for applciations (where you don't expect to recover the error), and thiserror is best for libraries because it gives you more detail about what went wrong.

The trade off is that thiserror involves more manual threading through of error structs.

Detail

@blaine ran into this while building the Fission server.

Coda

First off, thank you so much to the miantainers of rs-ucan for the work thus far. anyhow was probably the fastest & most pragmatic way to get things running.

[cdata]

Sounds good to me, contributions welcome here!

[cdata]

Anecdotally, we use thiserror in Noosphere (so soft preference for that crate)