worker: return back error strings to O

[gioelecerati]

Modifying worker.go:

• Appending the error message to the string that is currently getting sent back to the O and the Gateway, so that they can log the proper reasons of failure on the pipelines.

Modifying runner:

• Added an helper under util.py in the routes to handle pipeline exception. In this helper, known Exceptions or known patterns can return a humanized str as error and the specified status code for the exception. Otherwise, they return either a default error message and status code or the specified error string
• Potentially we could remove this helper and instead have this logic on the Gateway, to have humanized strings to be returned via api response to the requester.
• Currently not edited the llm pipeline, as I see it's returning dicts instead of string. I was unable to check if it's returning dict for a reason or not, to be updated later if we want to handle specific exceptions

[rickstaa]

@gioelecerati thanks for your pull request. Unfortunatelly, this was already implemented in PR #188. I had some last-minute changes stashed on my local machine, which I’ve just committed, and I also cleaned up the code a bit. I really like how you combined the handle_pipeline_exception into a single function. I was planning to implement this in a subsequent pull request (see #190).

Just keep in mind that I still have several other changes related to error handling that need to be reviewed (see PR #190). The current error handling is far from optimal, and it’s part of a broader project I’ve been working on to improve it (details here).

[rickstaa]

@gioelecerati I included your logic in https://github.com/livepeer/ai-worker/pull/188/commits and made you the author of that commit.