Enable parallel builds in CI

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: bdejong

.github/workflows/build.yml

@@ -31,7 +31,7 @@ jobs:
         run: cmake -B build -DCMAKE_BUILD_TYPE=Release
 
       - name: Build
-        run: cmake --build build --config Release
+        run: cmake --build build --config Release --parallel
 
       - name: Collect artifacts (macOS)
         if: runner.os == 'macOS'