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/dataflows/utils.py

@@ -1,10 +1,9 @@
-import os
 import re
-import json
-import pandas as pd
-from datetime import date, timedelta, datetime
+from datetime import date, datetime, timedelta
 from typing import Annotated
 
+import pandas as pd
+
 SavePathType = Annotated[str, "File path to save data. If None, data is not saved."]
 
 # Tickers can contain letters, digits, dot, dash, underscore, caret