fix(api): raise HTTPError instead of returning None on API errors

[MD-Mushfiqur123]

Resolves #820

Changes:

• Replaced _log_error() + return None pattern with r.raise_for_status() in all ApiClient methods
• Removed unused _log_error method
• Removed None-check in check_organization_exists (method now raises on HTTP errors)
• add_emission and _create_run already have try/except wrappers so they continue to handle errors gracefully (logging + returning False/None)
• CodeCarbonAPIOutput (used by EmissionsTracker) already wraps add_emission in try/except
• Updated tests to expect requests.HTTPError instead of None returns

[codecov]

Codecov Report

❌ Patch coverage is 53.84615% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.32%. Comparing base (987fbdf) to head (8fd5c58).

Files with missing lines	Patch %	Lines
codecarbon/core/api_client.py	53.84%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1213      +/-   ##
==========================================
+ Coverage   88.99%   89.32%   +0.33%     
==========================================
  Files          45       45              
  Lines        4316     4282      -34     
==========================================
- Hits         3841     3825      -16     
+ Misses        475      457      -18     

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[benoit-cty]

Thanks for your contribution. Can you improve the test coverage ?