Fix http_date function to correctly handle UTC time

[roscamaxim]

Problem

The http_date() function in xcover/utils.py incorrectly used mktime() to convert UTC time to a timestamp. Since mktime() interprets time tuples as local time, this caused the date header to be off by the local timezone offset (e.g., UTC+10 for Sydney). This resulted in authentication failures when clients were in different timezones.

In addition, the datetime.utcnow() is now deprecated and will be removed in a future version.

Solution

• Replacing datetime.utcnow() with the timezone-aware datetime.now(timezone.utc)
• Using direct string formatting with strftime() instead of mktime() and format_date_time()
• Ensuring the date header is properly formatted according to RFC 7231

Changes

• Fixed: http_date() function in xcover/utils.py to correctly handle UTC time
• Added: Unit test in tests/test_utils.py to verify the function works correctly
• Improved: README formatting by converting configuration options to a table
• Fixed: Typo in README (changed "poertry" to "poetry")
• CI fixed: updated GitHub Actions to the latest versions and resolved CI artifacts conflicts.

Testing

• Uses mocking to ensure deterministic testing
• Verifies the function calls datetime.now() with timezone.utc
• Confirms the output format is correct

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.43%. Comparing base (0d40c5e) to head (9e05ba2).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master       #5      +/-   ##
==========================================
- Coverage   95.47%   95.43%   -0.05%     
==========================================
  Files           7        7              
  Lines         221      219       -2     
==========================================
- Hits          211      209       -2     
  Misses         10       10              

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[roscamaxim]

@tyomo4ka had to push some substantial updates to ci.yaml and semgrep.yml to get all GH checks passing—please give those a quick look, too.