Add build artifacts to .gitignore and clean up executables

Co-authored-by: WenyinWei <[email protected]>

Author: Copilot

.gitignore

@@ -40,6 +40,12 @@
 # debug information files
 *.dwo
 
-# Build directories
-.xmake/
-build/
+# Build directories
+.xmake/
+build/
+
+# Example executables
+simple_standard_parallelism
+standard_parallelism_demo
+test_standard_parallelism
+parallelism_integration_demo