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 91.24%. Comparing base (0aeb818) to head (c15c563).

Additional details and impacted files

@@            Coverage Diff             @@
##            devel    #3175      +/-   ##
==========================================
- Coverage   91.27%   91.24%   -0.03%     
==========================================
  Files         204      204              
  Lines        8973     8973              
==========================================
- Hits         8190     8187       -3     
- Misses        783      786       +3     

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[NgoQuocViet2001]

Rebased onto current devel and resolved the upstream discovery-test changes while preserving the USE_RELATIVE_PATHS regression.

Focused Windows/MSVC validation passed for both the default and relocated relative modes: 22 test names matched the CTest listing, 22 matched TEST_LIST, and the relocated tests ran successfully. AppVeyor is also green across all 5 jobs.