perf(tests): stop paying the 0.5s serve_forever poll on every teardown

conftest.py

@@ -4,6 +4,32 @@
 module load time, which is only installed in the dedicated CI job. Ignore that
 directory during normal collection so the suite runs without the native
 toolchain. The Hypothesis property tests under ``tests/fuzz/`` are unaffected.
+
+The suite also stands hundreds of throwaway ``http.server`` instances in for
+provider endpoints, every one of them started as
+``threading.Thread(target=server.serve_forever, daemon=True)``.
+``socketserver.BaseServer.serve_forever`` only checks its stop flag once per
+``poll_interval`` seconds, and ``shutdown()`` blocks until that next check, so
+each teardown pays up to the 0.5s default. No call site in this repository
+passes the argument, so that default is paid several hundred times per run and
+dominates the wall clock: shortening it takes the suite from about eleven
+minutes to about one, with no change to what is asserted.
+
+This overrides the default rather than the call sites because a mocked server
+in ``tests/test_telemetry.py`` pins production ``serve()`` to invoking
+``serve_forever()`` with no arguments.
 """
 
+import socketserver
+
 collect_ignore = ["fuzz"]
+
+_ORIGINAL_SERVE_FOREVER = socketserver.BaseServer.serve_forever
+
+
+def _serve_forever(self, poll_interval: float = 0.01):
+    """Serve with a short stop-flag poll so ``shutdown()`` returns promptly."""
+    return _ORIGINAL_SERVE_FOREVER(self, poll_interval)
+
+
+socketserver.BaseServer.serve_forever = _serve_forever

tests/test_test_server_poll_interval.py

@@ -0,0 +1,35 @@
+"""Regression contracts for the pytest-only server polling override."""
+
+import socketserver
+
+import conftest
+
+
+def test_default_test_server_poll_interval_is_short(monkeypatch):
+    calls = []
+    sentinel = object()
+
+    def fake_serve_forever(server, poll_interval=0.5):
+        calls.append((server, poll_interval))
+        return sentinel
+
+    monkeypatch.setattr(conftest, "_ORIGINAL_SERVE_FOREVER", fake_serve_forever)
+    server = object()
+
+    assert conftest._serve_forever(server) is sentinel
+    assert calls == [(server, 0.01)]
+    assert socketserver.BaseServer.serve_forever is conftest._serve_forever
+
+
+def test_explicit_test_server_poll_interval_is_preserved(monkeypatch):
+    calls = []
+
+    def fake_serve_forever(server, poll_interval=0.5):
+        calls.append((server, poll_interval))
+
+    monkeypatch.setattr(conftest, "_ORIGINAL_SERVE_FOREVER", fake_serve_forever)
+    server = object()
+
+    conftest._serve_forever(server, poll_interval=0.25)
+
+    assert calls == [(server, 0.25)]