test: Add unit tests for src.runtime.robotics.load_unitree

[Wanbogang]

Summary

This PR adds comprehensive unit tests for the load_unitree function in src/runtime/robotics.py. This function is responsible for initializing the Unitree robot's network communication channel and is critical for startup in single/multi modes involving Unitree robots.

Details

• Adds tests for successful initialization scenario.
• Adds tests for failure scenario (when ChannelFactoryInitialize raises an exception).
• Adds test for the case when unitree_ethernet is None.
• Adds tests to verify logging behavior in all scenarios.
• Uses sys.modules patching to mock external dependencies like unitree.unitree_sdk2py.core.channel.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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