A sanctioned GIL acquisition operation, identifying why a
monarch_with_gil/monarch_with_gil_blocking site takes the GIL. Each
variant names one distinct operation so is_control_plane_allowed can
classify it. There is deliberately no catch-all: a new GIL site must add a
variant and classify it, or the code will not compile.
Force one unsanctioned control-plane GIL acquisition and count it, for the
negative fitness test. Runs on a freshly ControlPlane-tagged thread and
routes through check_gil_site so the real gating is exercised; the
debug-build debug_assert panic is swallowed so the increment sticks (in
release builds there is no assert and the counter bumps directly).
A test function that sleeps indefinitely in a loop.
This is used for testing signal handling in signal_safe_block_on.
The function will sleep forever until interrupted by a signal.