chore(lint): make the repository ruff-clean under the strict select

Clear the deferred full-repo lint backlog so the whole tree passes the strict
ruff select (E,W,F,I,B,UP,C4,SIM). Mechanical fixes dominate: import sorting,
pep585/604 annotations, dropped dead imports, and whitespace. The few semantic
changes are behavior-preserving: declare __all__ on the agent_utils and
alpha_vantage re-export hubs; expand 'from x import *' to explicit names; use
immutable tuple defaults instead of mutable list defaults; contextlib.suppress
for try/except/pass; and narrow an over-broad assertRaises.

tradingagents/graph/checkpointer.py

@@ -7,9 +7,9 @@ from __future__ import annotations
 
 import hashlib
 import sqlite3
+from collections.abc import Generator
 from contextlib import contextmanager
 from pathlib import Path
-from typing import Generator
 
 from langgraph.checkpoint.sqlite import SqliteSaver