Add more APIs

[svilupp]

• Support for Fireworks.ai and Together.ai providers for fast and easy access to open-source models. Requires environment variables FIREWORKS_API_KEY and TOGETHER_API_KEY to be set, respectively. See the ?FireworksOpenAISchema and ?TogetherOpenAISchema for more information.

[codecov]

Codecov Report

Attention: Patch coverage is 40.00000% with 12 lines in your changes are missing coverage. Please review.

Project coverage is 91.70%. Comparing base (463a830) to head (a525c7b).

Files	Patch %	Lines
src/llm_openai.jl	33.33%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #80      +/-   ##
==========================================
- Coverage   92.27%   91.70%   -0.57%     
==========================================
  Files          36       36              
  Lines        1890     1905      +15     
==========================================
+ Hits         1744     1747       +3     
- Misses        146      158      +12     

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