Add get_payroll_tax_revenue function for correct payroll tax revenue

[arihantlodha-cmd]

Closes #1023.

Adds a dedicated get_payroll_tax_revenue function in aggregates.py and calls it from revenue() in place of the two inline calculations.

Previously payroll tax revenue was always computed as frac_tax_payroll * iit_payroll_tax_revenue, which assumes payroll taxes are embedded in the estimated income and payroll tax functions and separated out via the frac_tax_payroll series. As noted in the issue, that is incorrect when a user instead models payroll taxes explicitly through tau_payroll (and excludes them from etr_params/mtrx_params/mtry_params). The new function branches on tau_payroll:

• if np.any(tau_payroll != 0): payroll_tax_revenue = tau_payroll * w * L (aggregate labor summed across industries)
• otherwise (the default, tau_payroll == 0): the existing frac_tax_payroll * iit_payroll_tax_revenue

The two are identical when tau_payroll == 0, so default runs are unchanged (existing test_revenue still passes).

A few implementation choices, flagged for review:

• Named it get_payroll_tax_revenue rather than payroll_tax_revenue to match the module's get_* convention and to avoid shadowing the local payroll_tax_revenue variable inside revenue(). Happy to rename if you'd prefer.
• L arrives per-industry in revenue(), so aggregate labor income uses L.sum(-1).
• Consolidated to a single call after the SS/TPI branches rather than duplicating the calculation in each.

Testing

• Added test_get_payroll_tax_revenue covering both branches for SS and TPI.
• pytest tests/test_aggregates.py -m "not local and not benchmark" → 43 passed; ruff format --check . and ruff check . clean.

One question for maintainers: when payroll taxes are modeled via tau_payroll and excluded from the tax functions, iit_payroll_tax_revenue no longer contains payroll revenue, so iit_revenue = iit_payroll_tax_revenue - payroll_tax_revenue (and payroll's contribution to total_tax_revenue) may also need revisiting. I left those as-is to keep this PR scoped to the issue — glad to follow up if you'd like that handled here too.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (master@b0986ac). Learn more about missing BASE report.
⚠️ Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1184   +/-   ##
=========================================
  Coverage          ?   72.70%           
=========================================
  Files             ?       22           
  Lines             ?     5734           
  Branches          ?        0           
=========================================
  Hits              ?     4169           
  Misses            ?     1565           
  Partials          ?        0           

Flag	Coverage Δ
unittests	72.70% <100.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
ogcore/aggregates.py	100.00% <100.00%> (ø)

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[jdebacker]

@arihantlodha-cmd Thanks for this PR.

Regarding your question, yes, let's fix the calculation of iit_revenue. I think something like the following could work (placed before the total_tax_revenue = line):

payroll_tax_revenue = get_payroll_tax_revenue(
        w, L, iit_payroll_tax_revenue, p, method
    )
if np.any(p.tau_payroll != 0):
    iit_payroll_tax_revenue += payroll_tax_revenue
iit_revenue = iit_payroll_tax_revenue - payroll_tax_revenue

[jdebacker]

Also, please run make format to resolve formatting issues. Thanks!

[arihantlodha-cmd]

Thanks for the review! Addressed both points:

• Added the iit_revenue fix as suggested: iit_payroll_tax_revenue += payroll_tax_revenue when np.any(p.tau_payroll != 0), so the explicitly-modeled payroll revenue now flows into both total_tax_revenue and iit_revenue.
• Regenerated the test_revenue golden values, since its params use tau_payroll=0.5. Each new total equals the previous total plus payroll_tax_revenue (verified by construction); default tau_payroll==0 runs are unchanged.

Ran make format and synced with master, so the lint check passes now (ruff format --check ., ruff check ., linecheck all clean). Full test_aggregates.py passes (43).