Fix relative PRE_TEST discovery paths

[NgoQuocViet2001]

Description

Add an opt-in USE_RELATIVE_PATHS mode to catch_discover_tests for DISCOVERY_MODE PRE_TEST.

When enabled, the generated CTest include resolves the test executable, discovery script, working directory, and discovery cache relative to its own relocated build-tree location. This keeps the existing behavior unchanged by default, supports single- and multi-config generators, and requires CMake 3.24 for the path generator expressions. The option and version requirement are documented.

The regression relocates the build tree before first discovery, uses a generator-expression WORKING_DIRECTORY, verifies the discovered names, runs the actual tests, and cleans the generated discovery cache.

GitHub Issues

Closes #3051

Testing

• Single-config Ninja relocation before first discovery: 5/5 tests passed
• Multi-config Ninja/Zig in a path containing spaces: default and relocated relative modes both discovered 5 tests; relocated CTest passed
• CMake 3.23.3: default mode configured successfully; opt-in mode failed with the expected CMake 3.24 requirement
• Python syntax and git diff --check passed

AI assistance

Codex (GPT-5, autonomous) implemented and iteratively validated the change on behalf of @NgoQuocViet2001. The operator requested the contribution but did not manually author or line-by-line review the patch.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.12%. Comparing base (a15f718) to head (77c8a2f).

Additional details and impacted files

@@            Coverage Diff             @@
##            devel    #3175      +/-   ##
==========================================
+ Coverage   91.09%   91.12%   +0.03%     
==========================================
  Files         204      204              
  Lines        8922     8922              
==========================================
+ Hits         8127     8130       +3     
+ Misses        795      792       -3     

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