Fix retries on successful messages

[brucruz]

• Moved @Retry decorator to a separate fetch_with_response() function
• Prevented retries from duplicating bot replies on failure
• Improved error handling for JSON parsing and Wit.AI response

[Logerfo]

These changes don't fix the duplication issue, as it's probably being caused by an architecture flaw. Regardless of that, I think they make the code a little better, so I'm willing to accept it, as long as we keep the comments.

[Logerfo]

I appreciate having those comments, although the code is currently not being used, it provides useful context in case we need to provide those parameters to the vendor.