Adds mock interfaces to enable unit-testing and isolated benchmaking. (#4491)

# Description

Add mock interfaces for PhysX's TensorAPI views as well as for the base
asset/sensor abstractions. These are targeted for towards unit testing
and benchmarking without starting kit.

New Features:
- MockArticulationData & MockArticulation
- MockRigidObjectData & MockRigidObject
- MockRigidObjectCollectionData & MockRigidObjectCollection
- MockIMUData & MockIMU
- MockFrameTransformerData & MockFrameTransformer
- MockContactSensorData & MockContactSensor
- MockRigidBodyView - Mock for physx.RigidBodyView
- MockArticulationView - Mock for physx.ArticulationView
- MockRigidContactView - Mock for physx.RigidContactView
- Pre-configured factories for quadruped (12 DOFs) and humanoid (21
DOFs) robots
- Patching utilities (context managers and decorators) for easy test
setup
- Tests to ensure coverage is correct


## Type of change

- New feature (non-breaking change which adds functionality)
- Documentation update

## Checklist

- [x] I have read and understood the [contribution
guidelines](https://isaac-sim.github.io/IsaacLab/main/source/refs/contributing.html)
- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [x] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

---------

Signed-off-by: Kelly Guo <[email protected]>
Co-authored-by: Kelly Guo <[email protected]>

Author: AntoineRichard

docs/index.rst

@@ -99,6 +99,7 @@ Table of Contents
    source/tutorials/index
    source/how-to/index
    source/overview/developer-guide/index
+   source/testing/index
 
 
 .. toctree::

docs/source/testing/index.rst

@@ -0,0 +1,11 @@
+.. _testing:
+
+Testing
+=======
+
+This section covers testing utilities and patterns for Isaac Lab development.
+
+.. toctree::
+   :maxdepth: 2
+
+   mock_interfaces