Force per-test GC so leaked-stream warnings stay inside the scoped filters

The module-level filterwarnings marks only apply while a test in this file
is the active warning context, but v1's leaked memory streams sit in
reference cycles and were garbage-collected later: at pytest's
session-unconfigure unraisable sweep (every test in this file passed but
pytest exited 1 when run without xdist, e.g. -n 0 for --pdb debugging), or
during an unrelated test on the same worker, where the global
filterwarnings = ["error"] turned the deallocator warning into a failure
of that innocent test.

An autouse fixture now runs gc.collect() in each test's teardown, so the
deallocator warnings fire where the scoped ignores apply. Verified: every
previously failing single-test and full-file -n 0 invocation now exits 0,
and cross-file runs no longer misattribute the warnings.

Author: maxisbey

tests/shared/test_streamable_http.py

@@ -4,9 +4,10 @@
 entirely in process.
 """
 
+import gc
 import json
 import time
-from collections.abc import AsyncIterator
+from collections.abc import AsyncIterator, Iterator
 from contextlib import asynccontextmanager
 from dataclasses import dataclass, field
 from datetime import timedelta
@@ -70,6 +71,23 @@
     pytest.mark.filterwarnings("ignore:.*MemoryObject(Send|Receive)Stream:ResourceWarning"),
 ]
 
+
+@pytest.fixture(autouse=True)
+def _collect_leaked_streams() -> Iterator[None]:
+    """Garbage-collect each test's leaked memory streams inside its own teardown.
+
+    The filterwarnings marks above only apply while a test in this file is the
+    active warning context. The leaked streams sit in reference cycles, so without
+    a forced collection their deallocator warnings fire wherever the garbage
+    collector happens to run next: during an unrelated test (failing it, since the
+    global ``filterwarnings = ["error"]`` has no ignore there) or at pytest's
+    session-unconfigure unraisable sweep (exit code 1 after all tests passed when
+    running without xdist, e.g. ``-n 0`` for ``--pdb`` debugging).
+    """
+    yield
+    gc.collect()
+
+
 # Test constants
 SERVER_NAME = "test_streamable_http_server"
 INIT_REQUEST = {