South Carolina retirement deduction & military retirement deduction

Fixes #2926

Co-authored-by: Pinyan <[email protected]>

policyengine_us/parameters/gov/states/sc/tax/income/subtractions/retirement_deduction/age_threshold.yaml

@@ -0,0 +1,11 @@
+description: South Carolina allows filers above this age to be eligible for the retirement income deduction.
+metadata:
+  unit: year
+  label: South Carolina retirement income deduction age threshold
+  reference: 
+    - title: South Carolina State SECTION 12-6-1170(B)
+      href: https://www.scstatehouse.gov/code/t12c006.php
+    - title: Instructions for Form SC-1040 (line 3p)
+      href: https://dor.sc.gov/forms-site/Forms/IITPacket_2021.pdf#page=18
+values:
+  2021-01-01: 65

policyengine_us/parameters/gov/states/sc/tax/income/subtractions/retirement_deduction/older_amount.yaml

@@ -0,0 +1,11 @@
+description: South Carolina allows a retirement deduction that is capped at this amount.
+metadata:
+  unit: currency-USD
+  label: South Carolina capped retirement deduction amount
+  reference: 
+    - title: South Carolina State SECTION 12-6-1170(A)(1)
+      href: https://www.scstatehouse.gov/code/t12c006.php
+    - title: Instructions for Form SC-1040 (line 3p)
+      href: https://dor.sc.gov/forms-site/Forms/IITPacket_2021.pdf#page=18
+values:
+  2021-01-01: 10_000

policyengine_us/parameters/gov/states/sc/tax/income/subtractions/retirement_deduction/younger_amount.yaml

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+description: South Carolina allows a retirement deduction that is capped at this amount.
+metadata:
+  unit: currency-USD
+  label: South Carolina capped retirement deduction younger amount
+  reference: 
+    - title: South Carolina State SECTION 12-6-1170(A)(1) 
+      href: https://www.scstatehouse.gov/code/t12c006.php
+    - title: Instructions for Form SC-1040 (line 3p)
+      href: https://dor.sc.gov/forms-site/Forms/IITPacket_2021.pdf#page=18
+values:
+  2021-01-01: 3_000

policyengine_us/tests/policy/baseline/gov/states/sc/tax/income/subtractions/retirement_deduction/sc_retirement_deduction.yaml

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+- name: Case 1, both head and spouse age higher than 65. 
+  period: 2022
+  input:
+    people:
+      person1:
+        taxable_pension_income: 2_000
+        military_retirement_pay: 11_000
+        age: 70
+        is_tax_unit_head: true
+      person2:
+        taxable_pension_income: 1_000
+        military_retirement_pay: 4_000
+        age: 66
+        is_tax_unit_spouse: true
+    tax_units:
+      tax_unit:
+        members: [person1, person2]
+    households:
+      household:
+        members: [person1, person2]
+        state_code: SC
+  output:
+    sc_retirement_deduction: 1_000
+
+- name: Case 2, both head and spouse age less than 65. 
+  period: 2022
+  input:
+    people:
+      person1:
+        taxable_pension_income: 2_000
+        military_retirement_pay: 11_000
+        age: 54
+        is_tax_unit_head: true
+      person2:
+        taxable_pension_income: 1_000
+        military_retirement_pay: 4_000
+        age: 50
+        is_tax_unit_spouse: true
+    tax_units:
+      tax_unit:
+        members: [person1, person2]
+    households:
+      household:
+        members: [person1, person2]
+        state_code: SC
+  output:
+    sc_retirement_deduction: 0
+
+- name: Case 3, head age higher than 65, spouse age less than 65. 
+  period: 2022
+  input:
+    people:
+      person1:
+        taxable_pension_income: 5_000
+        military_retirement_pay: 6_000
+        age: 70
+        is_tax_unit_head: true
+      person2:
+        taxable_pension_income: 1_000
+        military_retirement_pay: 4_000
+        age: 50
+        is_tax_unit_spouse: true
+    tax_units:
+      tax_unit:
+        members: [person1, person2]
+    households:
+      household:
+        members: [person1, person2]
+        state_code: SC
+  output:
+    sc_retirement_deduction: 4_000
+

policyengine_us/variables/gov/states/sc/tax/income/subtractions/retirement_deduction/sc_military_retirement_income_deduction_survivor.py

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+from policyengine_us.model_api import *
+
+
+class sc_military_retirement_income_deduction_survivor(Variable):
+    value_type = float
+    entity = TaxUnit
+    label = "South Carolina military retirement income deduction for survivor"
+    defined_for = StateCode.SC
+    unit = USD
+    definition_period = YEAR

policyengine_us/variables/gov/states/sc/tax/income/subtractions/retirement_deduction/sc_retirement_deduction.py

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+from policyengine_us.model_api import *
+
+class sc_retirement_deduction(Variable):
+    value_type = float
+    entity = TaxUnit
+    label = "South Carolina retirement deduction"
+    defined_for = StateCode.SC
+    unit = USD
+    reference = ("https://www.scstatehouse.gov/code/t12c006.php", #SECTION 12-6-1170(A)(1)
+                 "https://dor.sc.gov/forms-site/Forms/IITPacket_2021.pdf#page=18"
+    )
+    definition_period = YEAR
+
+    def formula(tax_unit, period, parameters):
+        p = parameters(period).gov.states.sc.tax.income.subtractions.retirement_deduction
+        person = tax_unit.members
+        age = person("age", period)
+        head = person("is_tax_unit_head", period)
+        spouse = person("is_tax_unit_spouse", period)
+        head_or_spouse = head | spouse
+        # line 1 
+        max_deduction_allowed = where(age >= p.age_threshold, p.older_amount, p.younger_amount)
+        # line 2
+        military_retirement_pay = person("military_retirement_pay", period)
+        # line 3
+        retirement_deduction_available = max_(max_deduction_allowed - military_retirement_pay,0)
+        # line 4
+        retirement_income = person("taxable_pension_income", period)
+        # line 5
+        return tax_unit.sum(min_(retirement_deduction_available, retirement_income))
+