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.

tests/test_checkpoint_resume.py

@@ -1,12 +1,9 @@
 """Test checkpoint resume: crash mid-analysis, re-run resumes from last node."""
 
-import sqlite3
 import tempfile
 import unittest
-from pathlib import Path
 from typing import TypedDict
 
-from langgraph.checkpoint.sqlite import SqliteSaver
 from langgraph.graph import END, StateGraph
 
 from tradingagents.graph.checkpointer import (