Patch to work with latest OG-Core

[jdebacker]

This PR patches OG-MYS to work with the latest OG-Core release.

To do this, references to surv_rate are removed and rho is made into a 2-dimensional object.

Note: tests will not pass until OG-USA is updated via this PR.

[codecov-commenter]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (cfb084a) 80.35% compared to head (9bb37ea) 79.82%.

Files	Patch %	Lines
ogmys/demographics.py	80.00%	2 Missing ⚠️
ogmys/income.py	95.45%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main      #12      +/-   ##
==========================================
- Coverage   80.35%   79.82%   -0.53%     
==========================================
  Files           9       10       +1     
  Lines         682      570     -112     
==========================================
- Hits          548      455      -93     
+ Misses        134      115      -19     

Flag	Coverage Δ
unittests	79.82% <93.87%> (-0.53%)	⬇️

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[jdebacker]

@rickecon This PR is ready for your review.

[rickecon]

Thanks @jdebacker. This PR looks great. Merging now.