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/__init__.py

@@ -1,3 +1,4 @@
+import contextlib
 import warnings
 
 # Load .env files at package import so DEFAULT_CONFIG's env-var overlay
@@ -20,10 +21,8 @@ except ImportError:
 # subclassed warning categories. To suppress a specific warning we must
 # install our filter AFTER langchain-core has installed its own, so import
 # it first. The package is a guaranteed transitive dep via langgraph.
-try:
+with contextlib.suppress(ImportError):
     import langchain_core  # noqa: F401
-except ImportError:
-    pass
 
 # langgraph-checkpoint 4.0.3 calls Reviver() at module load without an
 # explicit allowed_objects, which triggers a noisy pending-deprecation