Look into using external types for errors

[thunderbiscuit]

Uniffi allows us to use types that are defined externally and don't require wrapping directly using a fairly simply workflow.

See https://mozilla.github.io/uniffi-rs/latest/types/remote_ext_types.html#remote-types.

We successfully leveraged this for LogLevel, and I suspect that this might also work for some of our errors! Needs a bit of investigating though.