test: system tests for Fedora compatibility

[rmiki-dev]

This PR is a sub-issue of the initial System tests PR #78.

Due to cross-platform compatibility issues encountered in the original PR, I am splitting the implementation by platform. This specific PR focuses on stabilizing and enabling the system tests for Fedora builds.

Subsequent PRs will be submitted for macOS and Windows platforms/architectures once this baseline is merged.

Relates to #78

[gemini-code-assist]

Code Review

This pull request refactors the existing test suite by extracting common helper functions into a new tests/utils.sh file and significantly expands test coverage with several new integration scripts. These new tests cover various scenarios including delta paths, fuzzy renames, multiple old layers, source prefixes, and CLI error handling. Feedback highlights a potentially dangerous directory deletion in the Makefile, a bug in the sparse file creation logic within the utility script, and a portability improvement for temporary directory creation.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.60%. Comparing base (694288b) to head (88a378b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #81      +/-   ##
==========================================
+ Coverage   68.94%   75.60%   +6.66%     
==========================================
  Files          10       10              
  Lines        1111     1111              
==========================================
+ Hits          766      840      +74     
+ Misses        232      159      -73     
+ Partials      113      112       -1     

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