test: use thread polling instead of fixed sleep for Windows cleanup

Instead of waiting a fixed 5+ seconds, poll for proxy threads to finish
with gc.collect() calls. This is faster on typical runs (exits as soon
as threads are gone) while still having a 5s timeout for robustness.

Author: rodrigo.nogueira

tests/test_proxy_functional.py

@@ -89,21 +89,21 @@ def secure_proxy_url(tls_certificate_pem_path: str) -> Iterator[URL]:
             port=proxy_instance.flags.port,
         )
 
-    # On Windows, proxy.py uses threaded mode which can leave sockets in
-    # a state where they haven't been fully released when GC runs during
-    # pytest cleanup. A longer delay + multiple gc.collect() passes ensures
-    # the proxy threads finish cleanup before pytest's unraisableexception
-    # plugin collects warnings.
-    # TEMPORARY: Testing with delays before AND after gc.collect()
     if os.name == "nt":
         import gc
+        import threading
         import time
 
-        time.sleep(5)
-        gc.collect()
-        gc.collect()
-        gc.collect()
-        time.sleep(1)
+        deadline = time.monotonic() + 5.0
+        while time.monotonic() < deadline:
+            gc.collect()
+            proxy_threads = [
+                t for t in threading.enumerate()
+                if "proxy" in t.name.lower() or "acceptor" in t.name.lower()
+            ]
+            if not proxy_threads:
+                break
+            time.sleep(0.05)
 
 
 @pytest.fixture