test: fix salvage test imports; drop WAL worker-thread test superseded by read pool

- tests/cron/test_sessiondb_init_hang.py: add threading/time imports the
  salvaged late-close regression tests rely on.
- tests/test_hermes_state.py: drop
  test_close_closes_wal_read_connection_created_on_worker_thread — main
  replaced per-thread WAL reader ownership with the pooled read-connection
  design (permits + checkout/return), so cross-thread reader draining no
  longer exists in the form the test asserted.

tests/cron/test_sessiondb_init_hang.py

@@ -21,6 +21,8 @@ suite stays free of timing flakes under parallel load.
 """
 
 import concurrent.futures
+import threading
+import time
 from unittest.mock import MagicMock, patch
 
 from cron.scheduler import run_job

tests/test_hermes_state.py

@@ -177,41 +177,6 @@ class TestConnectionLifecycle:
                     pass
             db.close()
 
-    def test_close_closes_wal_read_connection_created_on_worker_thread(
-        self, tmp_path
-    ):
-        """SessionDB.close() must drain read conns created by other threads."""
-        from hermes_cli.sqlite_safe_read import has_live_connection
-
-        db_path = tmp_path / "state.db"
-        db = SessionDB(db_path=db_path)
-        db._wal_active = True
-        opened = threading.Event()
-        release = threading.Event()
-        errors = []
-
-        def open_read_connection():
-            try:
-                assert db._get_read_conn() is not None
-                opened.set()
-                release.wait(timeout=10)
-            except BaseException as exc:
-                errors.append(exc)
-                opened.set()
-
-        worker = threading.Thread(target=open_read_connection)
-        worker.start()
-        assert opened.wait(timeout=10)
-        assert not errors
-
-        db.close()
-        assert has_live_connection(db_path) is False
-
-        release.set()
-        worker.join(timeout=10)
-        assert not worker.is_alive()
-        assert not errors
-
     def test_read_only_close_never_requests_wal_checkpoint(self, tmp_path):
         db_path = tmp_path / "state.db"
         writable = SessionDB(db_path=db_path)