feat(lerobot): add ONNX export

[kainotkai]

Summary

This PR adds the ability to export LeRobot Policies, specifically ACT, into ONNX. It does this by following the generic Schola Model.

We call ACT's select action to build the ONNX graph. Sometimes in ACT, we have temporal ensemble, where we average out both past and current predictions before we select an action. To support this, we model temporal ensemble as recurrent state.

Related issues

Type of change

• Bug fix
• New feature or enhancement
• Documentation
• Refactor or internal cleanup
• Other (describe below)

Changes

Added support for LeRobot ACT ONNX export.

Testing

Python (Resources/python, Test)

• Installed test dependencies: pip install --group test -e "./Resources/python[all]"
• Ran: python -m pytest Test --import-mode=importlib -n 0
• Not applicable

Unreal C++ (Source)

• Built / recompiled the project after Unreal Engine changes
• Ran relevant automation tests (editor or pytest on Windows; see CONTRIBUTING.md)
• Not applicable

Checklist

• Code follows project style (Unreal coding standard for C++; Black for Python)
• Comments / docstrings added or updated where behavior is non-obvious
• README or Sphinx docs updated if user-facing behavior changed
• No unrelated changes included in this PR
• Appropriate license headers added to new files