fix(funasr): sanitize system Python environment

[LauraGPT]

Summary

• remove inherited embedded-Python path variables when QuQu uses a system Python
• add a focused node:test regression test and npm run test:unit entry point

Context

In the system-Python branch, buildPythonEnvironment() starts by copying process.env. It previously avoided assigning embedded values, but did not remove existing PYTHONHOME, PYTHONPATH, LD_LIBRARY_PATH, or DYLD_LIBRARY_PATH entries inherited from the launcher or an earlier runtime setup.

Those stale paths can make the selected system Python fail before the model-download script starts, commonly with ModuleNotFoundError: No module named 'encodings'.

The original environment handling reported in #61 is already improved on main compared with the v1.0.1 tag. This PR adds the remaining defensive cleanup plus a regression test so the failure does not return through inherited process state.

Verification

• npm run test:unit (1 passed)
• git diff --check

Related to #61.