Fix #76: -Wsign-conversion is redundant

[leftibot]

Automated fix by @leftibot.

What changed

Fix #76: Remove redundant -Wsign-conversion from CLANG_WARNINGS
-Wconversion already implies -Wsign-conversion for both GCC and Clang,
making the explicit -Wsign-conversion flag redundant in the CLANG_WARNINGS
list. Since GCC_WARNINGS inherits from CLANG_WARNINGS, this removal
applies to both compilers. Added a regression test to prevent
reintroduction of the redundancy.
Co-Authored-By: Claude Opus 4.6 (1M context) noreply@anthropic.com

Files

 cmake/CompilerWarnings.cmake                |  1 -
 test/CMakeLists.txt                         |  5 +++++
 test/cmake/test_no_redundant_warnings.cmake | 34 +++++++++++++++++++++++++++++
 3 files changed, 39 insertions(+), 1 deletion(-)

Closes #76

Triggered by @lefticus.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 20.50%. Comparing base (c61d47f) to head (2750021).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #149   +/-   ##
=======================================
  Coverage   20.50%   20.50%           
=======================================
  Files           5        5           
  Lines         239      239           
  Branches      111      113    +2     
=======================================
  Hits           49       49           
+ Misses        186      184    -2     
- Partials        4        6    +2     

Flag	Coverage Δ
Linux	18.36% <ø> (ø)
Windows	21.02% <ø> (ø)
macOS	18.87% <ø> (ø)

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[lefticus]

@leftibot remove the tests, those are unnecessary for this kind of PR

[leftibot]

Addressed review feedback from @lefticus. New commits:

2750021 Address review: remove redundant warning regression test