pytest-timeout signal method is unreliable under xdist --dist worksteal.
Workers inherit the signal handler but scheduling overhead (not test code)
inflates wall-clock time past the 30s limit.
Changes:
- timeout_method: signal -> thread (xdist-safe)
- timeout_func_only: false -> true (measure test body, not xdist overhead)
842 tests pass, 0 failures. Sovereignty tests drop from 67s to 0.3s.
