Fix capture loading from worker threads

[Mirochill]

Fixes #2.

Summary:

• create and set an event loop when capture parsing runs in a worker thread without one
• pass that loop explicitly to PyShark FileCapture and close it when parse_capture owns it
• add tests for worker-thread loop setup and FileCapture eventloop wiring

Validation:

• git diff --check
• git diff --cached --check
• git diff --check HEAD~1..HEAD
• Not run locally: pytest / TUI runtime / PyShark capture runtime