Add bench_reference.cpp

Also update snake case script for nanobench symbols

tools/check_snake_case.py

@@ -66,6 +66,8 @@ def check_snake_case_violations(filepath, check_new_only=True):
     exclusions = [
         # C++ standard library and common libraries
         r"\b(std::|weaseljson|simdutf|doctest)",
+        # Nanobench library API (external camelCase API)
+        r"\b(nanobench::|doNotOptimizeAway|minEpochIterations)\b",
         # Template parameters and concepts
         r"\b[A-Z][a-zA-Z0-9_]*\b",
         # Class/struct names (PascalCase is correct)