fix(streaming): raise on thread error events

[majiayu000]

Summary

• raise APIError when thread.* events include error payloads
• add regression coverage for thread error events (sync/async)

Testing

• PYTHONPATH=src pytest tests/test_streaming_errors.py -o addopts= -o filterwarnings= -p no:benchmark
• PYTHONPATH=src pytest -o addopts= -o filterwarnings= -p no:benchmark (fails: 502 from http://127.0.0.1:4010/audio/transcriptions in tests/api_resources/audio/test_transcriptions.py)