MuJoCo Simulator

[kdelmo1]

Description

This PR adds support for the MuJoCo physics engine to Scenic. It introduces a new simulator interface, a modular robot model, and procedural terrain generation.

Key Contributions:

• New Simulator: Added scenic.simulators.mujoco to interface with the MuJoCo physics engine.
• Robot Model: Implemented the Farm-ng Amiga agricultural robot with torque-controlled wheels and modular components.
• Procedural Environments: Added support for generating irregular terrain (hills) and crop rows.
• Tests: Added tests/simulators/mujoco/test_mujoco.py covering ground generation, terrain, and full robot integration (headless).
• Dependency Fix: Pinned antlr4-python3-runtime==4.9.3 to resolve a version conflict with Hydra/Omegaconf.

Issue Link

N/A (New Feature)

Checklist

• I have tested the changes locally via pytest and/or other means
• I have added or updated relevant documentation (Added README in examples folder)
• I have autoformatted the code with black and isort
• I have added test cases (if applicable)