chore: suppress upstream langgraph allowed_objects deprecation noise

langgraph-checkpoint 4.0.3 calls Reviver() at module load without
allowed_objects, printing a pending-deprecation warning at every
CLI start. The upstream patch is merged
(langchain-ai/langgraph#7743) but not released; no app-side seam
fixes it. Install a surgical filter in package init (message regex
+ PendingDeprecationWarning category). Remove when we bump past
langgraph-checkpoint 4.0.3.

tradingagents/__init__.py

@@ -0,0 +1,23 @@
+import warnings
+
+# langchain-core 1.3.3 calls surface_langchain_deprecation_warnings() in
+# its own __init__, which prepends default-action filters for its
+# 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:
+    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
+# warning from langchain-core 1.3.3 on every interpreter start. The fix
+# is already merged upstream (langchain-ai/langgraph#7743, 2026-05-08)
+# and will arrive in the next langgraph-checkpoint release. Remove this
+# block (and the langchain_core preload above) when we bump past it.
+warnings.filterwarnings(
+    "ignore",
+    message=r"The default value of `allowed_objects`.*",
+    category=PendingDeprecationWarning,
+)