Increase test coverage for utils, filters, and content_fetcher

[httpdss]

This PR improves test coverage focusing on three modules:

• struct_module/utils.py: Added tests for read_config_file, merge_configs, and get_current_repo (HTTPS/SSH variants and error handling).
• struct_module/filters.py: Added tests for slugify, get_default_branch (success and error with cache clearing), and get_latest_release (success, fallback to default branch, and error). Achieves 100% coverage for this module.
• struct_module/content_fetcher.py: Added tests for file://, https:// (cache behavior and HTTP error), githubhttps:// (pull on existing clone), github:// (fresh clone path), githubssh:// (missing file), unsupported scheme, and invalid GitHub path inputs.

Minor code change:

• Align internal URL parsing in ContentFetcher helpers to accept dispatcher-stripped paths (owner/repo/branch/file_path for GitHub; bucket/key for S3/GCS).

Results locally:

• All tests pass (71 passed).
• Overall coverage increased from ~65% to ~68%.
• Module-specific: filters 100%, utils 94%, content_fetcher 61%.

Next steps (optional):

• Add more ContentFetcher tests for git subprocess failure paths and S3/GCS ImportError/error handling.
• Introduce .coveragerc and enforce a minimum coverage threshold in CI (e.g., --cov-fail-under=70) and/or Codecov config.

Please review and let me know if you want me to continue with the additional tests and CI guardrails in this PR or a follow-up.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.35%. Comparing base (42219a2) to head (5c470b6).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #89      +/-   ##
==========================================
- Coverage   67.98%   64.35%   -3.64%     
==========================================
  Files          26       18       -8     
  Lines        1718     1139     -579     
  Branches      222      197      -25     
==========================================
- Hits         1168      733     -435     
+ Misses        496      350     -146     
- Partials       54       56       +2     

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