Fix Ruff E402 errors in sinch_events server example

[matsk-sinch]

Summary

• remove the pre-import sys.path mutation from examples/sinch_events/server.py to satisfy Ruff E402
• preserve runnable example behavior by aligning imports across the Sinch Events example package to local module imports
• keep endpoint/controller wiring unchanged

Validation

• python3 -m ruff check .

Slack Thread