Add more robust error messaging

[MAsuamah]

Feedback from a customer:

In the typescript sdk when assembly.transcripts.submit returns an error it's just a string. Is there a way to tell if it's retriable or not (ie if there's a status code)?

E.g. differentiating between a bad file submitted on our end (where sending our request again wouldn't fix anything) vs an internal assembly error / throttling / etc (where we could presumably just try the same request again later)