Migrate random variables to use specific seed variables from dataset

This change moves all randomness generation from policyengine-uk to
policyengine-uk-data, following the pattern established in policyengine-us.

Each independent random decision now has its own seed variable to avoid
artificial correlations between unrelated stochastic processes.

Changes:
- Add 11 new seed variables (4 person-level, 4 benunit-level, 3 household-level):
  - is_disabled_for_benefits_seed
  - marriage_allowance_take_up_seed
  - is_higher_earner_seed
  - attends_private_school_seed
  - child_benefit_take_up_seed
  - child_benefit_opts_out_seed
  - pension_credit_take_up_seed
  - universal_credit_take_up_seed
  - first_home_purchase_seed
  - household_owns_tv_seed
  - tv_licence_evasion_seed

- Update all variables using random() to use their specific seed variable

This ensures reproducible simulations and allows the dataset to control
all stochastic elements of the model.

Related: policyengine-uk-data PR (must be merged first)

Author: MaxGhenis

.claude

@@ -0,0 +1 @@
+Subproject commit eec0a00faf6ea6d0357736a0e6bcdbe679119ed0

policyengine_uk/parameters/gov/dfe/extended_childcare_entitlement/takeup_rate.yaml

@@ -0,0 +1,9 @@
+description: Extended childcare entitlement take-up rate
+metadata:
+  unit: /1
+  period: year
+  reference:
+    - title: Empirical estimate from FRS data
+      href: https://github.com/PolicyEngine/policyengine-uk-data
+values:
+  2015-01-01: 0.812

policyengine_uk/parameters/gov/dfe/targeted_childcare_entitlement/takeup_rate.yaml

@@ -0,0 +1,9 @@
+description: Targeted childcare entitlement take-up rate
+metadata:
+  unit: /1
+  period: year
+  reference:
+    - title: Empirical estimate from FRS data
+      href: https://github.com/PolicyEngine/policyengine-uk-data
+values:
+  2015-01-01: 0.597

policyengine_uk/parameters/gov/dfe/universal_childcare_entitlement/takeup_rate.yaml

@@ -0,0 +1,9 @@
+description: Universal childcare entitlement take-up rate
+metadata:
+  unit: /1
+  period: year
+  reference:
+    - title: Empirical estimate from FRS data
+      href: https://github.com/PolicyEngine/policyengine-uk-data
+values:
+  2015-01-01: 0.563

policyengine_uk/parameters/gov/hmrc/tax_free_childcare/takeup_rate.yaml

@@ -0,0 +1,9 @@
+description: Tax-Free Childcare take-up rate
+metadata:
+  unit: /1
+  period: year
+  reference:
+    - title: Empirical estimate from FRS data
+      href: https://github.com/PolicyEngine/policyengine-uk-data
+values:
+  2015-01-01: 0.586

policyengine_uk/variables/contrib/labour/attends_private_school.py

@@ -76,6 +76,6 @@ def formula(person, period, parameters):
             * is_child
         )
 
-        value = random(person) < p_attends_private_school
+        value = person("attends_private_school_seed", period) < p_attends_private_school
 
         return value

policyengine_uk/variables/contrib/labour/attends_private_school_seed.py

@@ -0,0 +1,8 @@
+from policyengine_uk.model_api import *
+
+
+class attends_private_school_seed(Variable):
+    value_type = float
+    entity = Person
+    label = "Random seed for private school attendance"
+    definition_period = YEAR

policyengine_uk/variables/gov/dcms/bbc/tv_licence/tv_licence_evasion_seed.py

@@ -0,0 +1,8 @@
+from policyengine_uk.model_api import *
+
+
+class tv_licence_evasion_seed(Variable):
+    value_type = float
+    entity = Household
+    label = "Random seed for TV licence evasion"
+    definition_period = YEAR

policyengine_uk/variables/gov/dcms/bbc/tv_licence/would_evade_tv_licence_fee.py

@@ -12,4 +12,4 @@ class would_evade_tv_licence_fee(Variable):
 
     def formula(household, period, parameters):
         evasion_rate = parameters(period).gov.dcms.bbc.tv_licence.evasion_rate
-        return random(household) <= evasion_rate
+        return household("tv_licence_evasion_seed", period) <= evasion_rate

policyengine_uk/variables/gov/dfe/extended_childcare_entitlement/extended_childcare_take_up_seed.py

@@ -0,0 +1,8 @@
+from policyengine_uk.model_api import *
+
+
+class extended_childcare_take_up_seed(Variable):
+    value_type = float
+    entity = BenUnit
+    label = "Random seed for extended childcare take-up"
+    definition_period = YEAR