Allow demographics to vary across income groups

[jdebacker]

This PR updates OG-Core to allow demographic parameters (mortality, fertility, immigration rates -- and the resulting population distribution) to vary across lifetime income group (J).

With income specific demographics, the $\lambda_j$ are redefined and no longer will represent the shares of each income group in a model period. Rather, the $\lambda_j$ will define the fraction of new "births" into each lifetime income group.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 69.80392% with 77 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.66%. Comparing base (d907c8e) to head (9d1d18a).

Files with missing lines	Patch %	Lines
ogcore/demographics.py	67.21%	60 Missing ⚠️
ogcore/parameters.py	40.00%	9 Missing ⚠️
ogcore/output_plots.py	62.50%	3 Missing ⚠️
ogcore/utils.py	66.66%	3 Missing ⚠️
ogcore/parameter_plots.py	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1165      +/-   ##
==========================================
- Coverage   72.92%   72.66%   -0.26%     
==========================================
  Files          22       22              
  Lines        5525     5725     +200     
==========================================
+ Hits         4029     4160     +131     
- Misses       1496     1565      +69     

Flag	Coverage Δ
unittests	72.66% <69.80%> (-0.26%)	⬇️

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

Files with missing lines	Coverage Δ
ogcore/SS.py	79.02% <ø> (ø)
ogcore/TPI.py	36.29% <100.00%> (ø)
ogcore/aggregates.py	100.00% <100.00%> (ø)
ogcore/household.py	90.77% <100.00%> (ø)
ogcore/output_tables.py	88.15% <100.00%> (ø)
ogcore/parameter_plots.py	78.64% <66.66%> (-0.18%)	⬇️
ogcore/output_plots.py	87.60% <62.50%> (-0.53%)	⬇️
ogcore/utils.py	83.56% <66.66%> (-0.39%)	⬇️
ogcore/parameters.py	81.76% <40.00%> (-0.49%)	⬇️
ogcore/demographics.py	58.41% <67.21%> (+5.04%)	⬆️

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[jdebacker]

All tests pass locally:

(base) jason.debacker@MacBookPro OG-Core % uv run pytest
============================= test session starts ==============================
platform darwin -- Python 3.12.12, pytest-9.0.3, pluggy-1.6.0
rootdir: /Users/jason.debacker/repos/OG-Core
configfile: pyproject.toml
testpaths: tests
plugins: cov-7.1.0, xdist-3.8.0
collected 643 items

tests/test_SS.py ..........................................              [  6%]
tests/test_TPI.py .........................................              [ 12%]
tests/test_aggregates.py ..........................................      [ 19%]
tests/test_basic.py ....                                                 [ 20%]
tests/test_demographics.py ....................                          [ 23%]
tests/test_elliptical_u_est.py .......                                   [ 24%]
tests/test_execute.py .                                                  [ 24%]
tests/test_firm.py ..................................................... [ 32%]
................                                                         [ 35%]
tests/test_fiscal.py ..........................                          [ 39%]
tests/test_household.py ................................................ [ 46%]
...                                                                      [ 47%]
tests/test_output_plots.py ............................................. [ 54%]
.....                                                                    [ 54%]
tests/test_output_tables.py ...................                          [ 57%]
tests/test_parameter_plots.py .......................................... [ 64%]
.                                                                        [ 64%]
tests/test_parameter_tables.py .......                                   [ 65%]
tests/test_parameters.py ................                                [ 68%]
tests/test_pensions.py ....................................              [ 73%]
tests/test_population_accounting.py ..                                   [ 74%]
tests/test_run_example.py ..                                             [ 74%]
tests/test_run_ogcore.py .                                               [ 74%]
tests/test_tax.py .....................................                  [ 80%]
tests/test_txfunc.py ...................................                 [ 85%]
tests/test_user_inputs.py .....^[[B....                                      [ 87%]
tests/test_utils.py .................................................... [ 95%]
...............................                                          [100%]
================ 643 passed, 82 warnings in 22030.20s (6:07:10) ================