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/llm_clients/api_key_env.py

@@ -11,10 +11,7 @@ prompts for it automatically instead of failing on first API call.
 
 from __future__ import annotations
 
-from typing import Optional
-
-
-PROVIDER_API_KEY_ENV: dict[str, Optional[str]] = {
+PROVIDER_API_KEY_ENV: dict[str, str | None] = {
     "openai":     "OPENAI_API_KEY",
     "anthropic":  "ANTHROPIC_API_KEY",
     "google":     "GOOGLE_API_KEY",
@@ -47,7 +44,7 @@ PROVIDER_API_KEY_ENV: dict[str, Optional[str]] = {
 }
 
 
-def get_api_key_env(provider: str) -> Optional[str]:
+def get_api_key_env(provider: str) -> str | None:
     """Return the env var name for `provider`'s API key, or None if not applicable.
 
     Unknown providers also return None — callers should treat that as