Fix Error Serialization with the addition od Display on Errors

[benalleng]

At the moment we just stringify all errors but ideally we would want to pass across the actual error types, However until uniffi 0.30 we had to choose between readable errors or errors that could be properly type cast. Until now all of our Errors are just the strigifiied versions, however, with the new uniffi release it looks as though we can add a simple Display trait on the errors to allow them to be stringified while also passing the actual error.

We started the discussion in #36