Refresh policyengine-us to 1.715.3

Latest PyPI release; satisfies the PolicyEngine US freshness check (main was
pinned to 1.715.2, now stale).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: MaxGhenis

pyproject.toml

@@ -22,7 +22,7 @@ classifiers = [
     "Programming Language :: Python :: 3.14",
 ]
 dependencies = [
-    "policyengine-us==1.715.2",
+    "policyengine-us==1.715.3",
     # policyengine-core 3.26.1 is the current 3.26.x runtime and includes the fix for
     # PolicyEngine/policyengine-core#482 (user-set ETERNITY inputs lost
     # after _invalidate_all_caches) and is required by policyengine-us 1.682.1+.