- Drop google_benchmark module dependency, wasn't really using it.
- Move benchmark models into test_data
- Rename benchmark => testspeed, make default output more like MJ testspeed.
- Update viewer to use new io functions and add get_data_into.
- Add "mjx-testspeed" and "mjx-viewer" bin scripts
PiperOrigin-RevId: 601277135
Change-Id: I782f666c58a96ac1a0a1c5ffc8ecf29d9fcd810f