fix(eval): close the parallel lane's per-item client

The subprocess worker built a fresh client per work item and never
closed it. Pool workers are reused across items, so each one
accumulated a live transport per item for the life of the sweep.

turnstone/eval/core.py

@@ -822,6 +822,21 @@ def _run_and_score_subprocess(params: dict[str, Any]) -> dict[str, Any]:
     case: dict[str, Any] = params["case"]
     run_tokens = 0
 
+    try:
+        return _run_and_score_with(client, params, case, run_tokens)
+    finally:
+        # Pool workers are reused across work items, so an unclosed
+        # client accumulates one live transport per item inside the
+        # worker process for the life of the sweep.
+        with contextlib.suppress(Exception):
+            client.close()
+
+
+def _run_and_score_with(
+    client: Any, params: dict[str, Any], case: dict[str, Any], run_tokens: int
+) -> dict[str, Any]:
+    """The body of :func:`_run_and_score_subprocess`, client lifetime
+    owned by the caller."""
     try:
         run_result = _run_single_test(
             client=client,