Fix MacOSARM64 CI: update Google Benchmark and disable its -Werror

[Auburn]

Problem

CI has been failing since September on MacOSARM64-Clang, in the CMake Install Release step. No code change caused it: the last passing commit is ba93f17, and the first failure was 06969a1, a .gitignore change.

macos-latest moved to the macos-26-arm64 image, which uses AppleClang 21 / Xcode 26.6. Its libc++ now annotates std::mutex for Clang's thread safety analysis. Google Benchmark 1.5.5 forces -Werror on Release builds, and its own Mutex wrapper annotations are disabled because its feature check fails. Clang therefore reports the wrapper as holding and releasing a mutex it doesn't own:

_deps/benchmark-src/src/mutex.h:79:40: error: mutex 'mut_' is still held at the end of function [-Werror,-Wthread-safety-analysis]
_deps/benchmark-src/src/mutex.h:80:34: error: releasing mutex 'mut_' that was not held [-Werror,-Wthread-safety-analysis]

Upstream issue: google/benchmark#2263. The fix (google/benchmark#2275) is merged but not in a release yet.

Fix

• Update Google Benchmark from 1.5.5 to 1.9.5, the latest release.
• Set BENCHMARK_ENABLE_WERROR OFF (an option added after 1.5.5), so warnings in the third-party library can't fail our build. Only the benchmark dependency is affected; FastNoise2's own flags are unchanged.

Testing

• Reproduced locally: Emscripten's libc++ with -D_LIBCPP_ENABLE_THREAD_SAFETY_ANNOTATIONS hits the same two mutex.h errors with 1.5.5. Newer Clang also hits -Wc2y-extensions errors in 1.5.5.
  • With this change, the same build compiles FastNoiseBenchmark with no errors or warnings.
• Builds and runs: FastNoiseBenchmark and FastNoiseCpp11Test build and run with MSVC, clang-cl, GCC 13.3 and Clang 18.1.
• Continuous benchmarking: I ran the benchmark with the same flags FastNoise2Benchmarking uses. The JSON still contains <name>_median entries with items_per_second, which is what generate_html_charts.py -f_median$ reads. The new _cv aggregate is filtered out by that pattern.
• Release packages: the dependency is still EXCLUDE_FROM_ALL, so nothing from it is installed into the CI packages, same as before.