chore: adopt run_uvicorn_in_thread from MAX-157, drop wait_for_server

Rebased onto MAX-157 (#2267) which landed run_uvicorn_in_thread with
two improvements over the helper this branch had:
  - Pre-binds socket + listen() before thread start: port is known
    immediately, no polling loop, kernel queues early connections
  - interface="asgi3": skips uvicorn's asyncio.iscoroutinefunction
    autodetect, which Python 3.14 deprecates (cleaner than
    catch_warnings)

Kept this branch's gc.collect() + ResourceWarning suppression in the
finally — MAX-157's single WS smoke test didn't need it, but the SSE
abrupt-disconnect test patterns here do.

Also removed wait_for_server — MAX-155 (#2277) converted its last
caller (test_integration.py) to in-memory transport.

Author: maxisbey

tests/test_helpers.py

@@ -3,7 +3,6 @@
 import gc
 import socket
 import threading
-import time
 import warnings
 from collections.abc import Generator
 from contextlib import contextmanager
@@ -68,30 +67,3 @@ def run_uvicorn_in_thread(app: Any, **config_kwargs: Any) -> Generator[str, None
         with warnings.catch_warnings():
             warnings.simplefilter("ignore", ResourceWarning)
             gc.collect()
-
-
-def wait_for_server(port: int, timeout: float = 20.0) -> None:
-    """Wait for server to be ready to accept connections.
-
-    Polls the server port until it accepts connections or timeout is reached.
-    This eliminates race conditions without arbitrary sleeps.
-
-    Args:
-        port: The port number to check
-        timeout: Maximum time to wait in seconds (default 5.0)
-
-    Raises:
-        TimeoutError: If server doesn't start within the timeout period
-    """
-    start_time = time.time()
-    while time.time() - start_time < timeout:
-        try:
-            with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
-                s.settimeout(0.1)
-                s.connect(("127.0.0.1", port))
-                # Server is ready
-                return
-        except (ConnectionRefusedError, OSError):
-            # Server not ready yet, retry quickly
-            time.sleep(0.01)
-    raise TimeoutError(f"Server on port {port} did not start within {timeout} seconds")  # pragma: no cover