chore: Add benchmark comparison files to .gitignore

- Add bench-old.txt and bench-new.txt to .gitignore
- These files are generated by make bench-compare for local benchmark comparisons

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: richardwooding

.gitignore

@@ -26,3 +26,7 @@ examples/*/main.exe
 
 # Coverage reports
 coverage.html
+
+# Benchmark comparison files
+bench-old.txt
+bench-new.txt