fix: Pin policyengine-us to >=1.592.4

The lockfile had 1.435.0 which uses a simplified StateGroup enum
(CONTIGUOUS_US, AK, HI, GU, PR, VI) without individual state codes,
causing test failures when passing state_code='CA'.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: anth-volk

pyproject.toml

@@ -13,7 +13,7 @@ dependencies = [
     "storage3>=0.8.1",
     "policyengine>=3.2.0",
     "policyengine-uk>=2.75.1",
-    "policyengine-us>=1.0.0",
+    "policyengine-us>=1.592.4",
     "pydantic>=2.9.2",
     "pydantic-settings>=2.6.0",
     "rich>=13.9.4",