Add Minnesota renter's credit

[PavelMakarchuk]

Summary

• add Minnesota renter's credit variables and parameters
• wire the credit into Minnesota refundable credits and the state property tax credit umbrella
• add regression and integration coverage for ordinary renter-credit cases

Testing

• python policyengine_us/tests/test_batched.py policyengine_us/tests/policy/baseline/gov/states/mn/tax/income/credits/mn_rent_constituting_property_taxes.yaml --batches 1
• python policyengine_us/tests/test_batched.py policyengine_us/tests/policy/baseline/gov/states/mn/tax/income/credits/mn_renters_credit_household_income.yaml --batches 1
• python policyengine_us/tests/test_batched.py policyengine_us/tests/policy/baseline/gov/states/mn/tax/income/credits/mn_renters_credit.yaml --batches 1
• python policyengine_us/tests/test_batched.py policyengine_us/tests/policy/baseline/gov/states/mn/tax/income/mn_integration.yaml --batches 1
• python policyengine_us/tests/test_batched.py policyengine_us/tests/policy/baseline/gov/states/mn/tax/income --batches 1
• python -m pytest policyengine_us/tests/policy/baseline/gov/tax/income/test_legacy_state_umbrellas.py -q

Fixes #7938

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (e8a542a) to head (e9579bd).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##              main     #7956    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
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  Files            1        10     +9     
  Lines           17       141   +124     
==========================================
+ Hits            17       141   +124     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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[DTrim99]

Found one issue to address:

[P2] Prorate assisted rent with AGI, not household income

In policyengine_us/variables/gov/states/mn/tax/income/credits/mn_renters_credit.py around lines 32-37, the assistance-paid-rent fraction is using mn_renters_credit_household_income, which is after age/disability/dependent/SEIU subtractions. Minn. Stat. 290.0693 Subd. 6(b) defines this fraction with adjusted gross income in both numerator and denominator, so older/disabled/dependent claimants in assisted facilities get under-credited here. Please base the proration ratio on the pre-subtraction household AGI/line-5 amount and add a test where assistance rent combines with an age or dependent subtraction.