fix: Properly type FIPS as string

Author: anth-volk

policyengine_us/tests/policy/baseline/household/demographic/geographic/county/county.yaml

@@ -1,8 +1,3 @@
-# Test runner in policyengine-core uses `numexpr.evaluate()` under the hood
-# to convert strings to expressions, where possible. This causes errors for
-# FIPS codes with leading zeros, EVEN WHEN DEFINED AS STRINGS. However, they do
-# work correctly in the code itself, as demonstrated with vectorized input 
-# in last test case.
 - name: County based on county FIPS for Nassau County, New York state
   period: 2025
   input:
@@ -17,6 +12,27 @@
   output:
     county: PHILADELPHIA_COUNTY_PA
 
+- name: County derived from county FIPS for Los Angeles County, California
+  period: 2025
+  input:
+    county_fips: "06037"
+  output:
+    county: LOS_ANGELES_COUNTY_CA
+
+- name: County equivalent for District of Columnbia
+  period: 2025
+  input:
+    county_fips: "11001"
+  output:
+    county: DISTRICT_OF_COLUMBIA_DC
+
+- name: FIPS for Mayagüez, Puerto Rico
+  period: 2025
+  input:
+    county_fips: "72097"
+  output:
+    county: MAYAGÜEZ_MUNICIPIO_PR
+
 - name: County FIPS for vectorized input
   period: 2025
   input:

policyengine_us/variables/input/geography.py

@@ -128,7 +128,7 @@ def formula(household, period, parameters):
 
 
 class county_fips(Variable):
-    value_type = int
+    value_type = str
     label = "County FIPS code"
     entity = Household
     definition_period = YEAR