fix: handle empty responses

[Danidapena]

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

Retries and tires fallback models when response is empty:

demo

PR review

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[codecov]

Codecov Report

❌ Patch coverage is 88.04348% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 84%. Comparing base (1854f73) to head (c84aabf).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@        Coverage Diff         @@
##           main   #66   +/-   ##
==================================
+ Coverage    84%   84%   +1%     
==================================
  Files         8     8           
  Lines       466   537   +71     
==================================
+ Hits        390   453   +63     
- Misses       76    84    +8     

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[k223kim]

@Danidapena Hey Daniela, looks really good! Just a couple things:

1. Can we handle errors for such failures (empty responses) so that users will know why it failed?
2. I don't think async calls are working. It throws such error:

sys:1: RuntimeWarning: coroutine 'LLM._async_chat' was never awaited