test: add blocking IO detector (#2924)

* test: add blocking IO detector

* test: add blocking IO probe option

* test: harden blocking IO probe lifecycle

* test: move blocking io detector to support

backend/tests/test_blocking_io_probe_integration.py

@@ -0,0 +1,22 @@
+from __future__ import annotations
+
+import time
+
+import pytest
+
+ORIGINAL_SLEEP = time.sleep
+
+
+def replacement_sleep(seconds: float) -> None:
+    return None
+
+
+def test_probe_survives_monkeypatch_teardown(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setattr(time, "sleep", replacement_sleep)
+    assert time.sleep is replacement_sleep
+
+
+@pytest.mark.no_blocking_io_probe
+def test_probe_restores_original_after_monkeypatch_teardown() -> None:
+    assert time.sleep is ORIGINAL_SLEEP
+    assert getattr(time.sleep, "__wrapped__", None) is None