The benchmark API captures per-frame data from the game loop, which is
bypassed when using step()-based simulation control. This warning
informs users to use Python's time module for headless performance
measurement instead.
Also adds test_headless_benchmark.py which verifies:
- step() and screenshot() don't produce benchmark frames
- Wall-clock timing for headless operations
- Complex scene throughput measurement
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
