Add 2023 Montana Tax Rules

[xianxinzhu]

Fixes #4187

[PavelMakarchuk]

Could you add the changes to the issue as you go through

[xianxinzhu]

• Add 2023 Form 2 references for the unchanged parameters.
• Update the net long-term capital gain tax rate.

[PavelMakarchuk]

For the capital gains tax:

• exclude the credit from the income tree for the year where it is repealed

• create a mt_capital_gains_tax (probably need an _indiv and _joint)

• add the value of this new variable to the mt_income_tax_before_non_refundable_credits (_indiv and _joint)

• in the income for the variable above, exclude capital gains from the income line: income = person("mt_taxable_income_indiv", period)

Make a bool parameter stating that capital gains should be taxed separately

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.17%. Comparing base (70fbb46) to head (5b7297f). Report is 8 commits behind head on master.

:exclamation: Current head 5b7297f differs from pull request most recent head e661fc1

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4352      +/-   ##
==========================================
+ Coverage   98.99%   99.17%   +0.17%     
==========================================
  Files        2454     2427      -27     
  Lines       35679    35185     -494     
  Branches      184      177       -7     
==========================================
- Hits        35322    34893     -429     
+ Misses        327      262      -65     
  Partials       30       30              

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[MaxGhenis]

tests failing

[PavelMakarchuk]

tests failing

Old tests, removed,