PhysicalAI MuJoCo SO-101 Plugin

Imported from https://github.com/MarkRedeman/physicalai-plugins,
packages/physicalai-mujoco-plugin, at commit
53bf606ef0f340a2a1821fc42a1ab6f44c33edf7 (PR #36).
The source repository distributes this package under Apache-2.0.
The original release history is preserved in CHANGELOG.md.

urdf/scenes/yahtzee/assets/wood_19.png is Wood_19-512x512.png from
"Tiny Texture Pack 2" by Screaming Brain Studios, released under CC0 1.0:
https://opengameart.org/content/tiny-texture-pack-2
