[MJCF] Add Actuator Grouping Based on Control Types

[ShravanTata]

Summary
Implement MuJoCo's native actuator grouping feature to organize actuators by their Control types from farms_core. This will enable selective enabling/disabling of actuator groups at the physics level and visual debugging.

Background
MuJoCo natively supports grouping actuators for selective enabling/disabling. This grouping provides both physics-level control and visual debugging benefits. We already have an enum for different Control types in farms_core

Proposed Change
Add support for grouping actuators based on their Control type enum values when defining the actuators in MuJoCo.

Benefits

• Provides selective enabling/disabling of actuator groups at physics level
• Improves visual debugging capabilities
• Backwards compatible—changes will be opaque to existing users
• Existing users will automatically benefit without code changes

Implementation Notes

• Use the existing Control type enum from farms_core
• Map each Control type to a corresponding MuJoCo actuator group
• Ensure backward compatibility is maintained

Tasks

• Map Control types to MuJoCo actuator groups
• Implement automatic group assignment when defining actuators
• Update documentation to describe the new feature
• Verify backward compatibility with existing code