Convert WIC float draws to bools to match other takeup variables

Remove draw variables; would_claim_wic and wic_nutritional_risk_imputed are
now simple data-read bools. is_wic_at_nutritional_risk gates imputed risk on
having a valid WIC category.

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

Author: baogorek

policyengine_us/variables/gov/usda/wic/is_wic_at_nutritional_risk.py

@@ -10,9 +10,8 @@ class is_wic_at_nutritional_risk(Variable):
     reference = "https://www.law.cornell.edu/uscode/text/42/1786#b_8"
 
     def formula(person, period, parameters):
-        draw = person("wic_nutritional_risk_draw", period)
         wic_reported = person("receives_wic", period)
+        imputed_risk = person("wic_nutritional_risk_imputed", period)
         category = person("wic_category", period)
-        risk = parameters(period).gov.usda.wic.nutritional_risk
-        imputed_risk = draw < risk[category]
-        return wic_reported | imputed_risk
+        has_wic_category = category != category.possible_values.NONE
+        return wic_reported | (imputed_risk & has_wic_category)

policyengine_us/variables/gov/usda/wic/wic_nutritional_risk_draw.py

@@ -0,0 +1,9 @@
+from policyengine_us.model_api import *
+
+
+class wic_nutritional_risk_imputed(Variable):
+    value_type = bool
+    entity = Person
+    label = "Imputed WIC nutritional risk"
+    definition_period = MONTH
+    default_value = True

policyengine_us/variables/gov/usda/wic/wic_nutritional_risk_imputed.py

@@ -6,9 +6,4 @@ class would_claim_wic(Variable):
     entity = Person
     label = "Would claim WIC"
     definition_period = MONTH
-
-    def formula(person, period, parameters):
-        draw = person("wic_takeup_draw", period)
-        category = person("wic_category", period)
-        takeup = parameters(period).gov.usda.wic.takeup
-        return draw < takeup[category]
+    default_value = True