🪲 BUG-#245: Fix TimeoutError not caught on Python 3.9/3.10

[FernandoCelmer]

Summary

• Import concurrent.futures.TimeoutError as FuturesTimeoutError
• Catch both TimeoutError and FuturesTimeoutError in execute_with_retry (line 136) and _execute_with_timeout (line 181)
• Re-raise as TimeoutError() from None for clean traceback

Problem

On Python 3.9/3.10, concurrent.futures.TimeoutError is a separate class that does not inherit from builtins.TimeoutError. The code only caught TimeoutError (builtin), so future.result(timeout=N) raised an uncaught exception that bypassed retry logic.

On Python 3.11+, they unified the classes so the bug was invisible.

Tests

• test_timeout_expired_marks_task_failed — real timeout with sleep(5) and timeout=1
• test_futures_timeout_error_is_caught — mocks _execute_with_timeout to raise FuturesTimeoutError directly

Test plan

• All 3 timeout tests pass
• ruff lint + format pass with .code_quality/ruff.toml

Closes #245