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

[AbdelhamidKhald]

Summary

Relates to #820

Problem

ApiClient methods silently return None, False, or [] when API calls fail. This makes it impossible for callers to distinguish between "API returned an error" and "no data exists", leading to confusing TypeError exceptions downstream (e.g., iterating over None).

Solution

Added response.raise_for_status() at the end of _log_error(), so all API methods now raise requests.exceptions.HTTPError after logging the error details. Removed the now-unreachable return None/False/[] statements.

Safety

All existing callers already handle exceptions properly:

• CodeCarbonAPIOutput.live_out() / .out() — wrapped in try/except Exception
• _create_run() — has except requests.exceptions.ConnectionError and except Exception
• add_emission() — has except Exception
• CLI commands — all go through main() which has a global try/except Exception

Changes

• codecarbon/core/api_client.py: Added response.raise_for_status() to _log_error(); removed 13 unreachable return statements and 1 dead None guard
• tests/test_api_call.py: Added test_call_api_error verifying HTTPError is raised on 500/400 responses

Testing

• All 11 existing + new tests pass
• black formatting: clean
• ruff linting: clean
• Verified all caller exception handling paths

Checklist

• Tests pass locally
• Linter passes
• Follows contribution guidelines
• Changes are minimal and focused

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.07%. Comparing base (db0d749) to head (f925406).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1089      +/-   ##
==========================================
+ Coverage   78.19%   79.07%   +0.88%     
==========================================
  Files          38       38              
  Lines        3637     3623      -14     
==========================================
+ Hits         2844     2865      +21     
+ Misses        793      758      -35     

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