Backdate Colorado TANF parameters to 1997

[hua7450]

Summary

Backdates Colorado TANF (Colorado Works) parameters to 2013 and improves code quality.
Closes #7506

Changes

• Parameters backdated: 9 files, ~71 date entries added (2013-07-01 values from 9 CCR 2503-6)
• New values added: 2024-07-01 grant standard additional child ($86)
• Bug fix: Grant standard additional child corrected from $82 to $86 (confirmed by 2 CCR versions + Cornell Law)
• Reference fixes: All 9 parameter files -- added specific CCR section numbers, descriptive titles
• Formula improvements: Removed redundant min_() in co_tanf.py, added defined_for guard
• Tests added: 104 tests across 10 files (historical eras, boundary conditions, edge cases)

Regulatory Sources

• 9 CCR 2503-6, Colorado Works Program (2022 version) -- Grant/need standard tables (Section 3.606.2.F)
• 9 CCR 2503-6, Colorado Works Program (2024 version) -- Updated grant standard tables (Section 3.606.2.F)

Review Summary

• Review: 1 round, COMMENT severity (no request-changes issues from this PR)
• PDF audit: 147 parameter values verified against source PDFs, 0 mismatches
• Items verified correct: Grant/need standard tables (all 3 eras), additional child amounts, pregnancy allowance, earned income disregards, child support handling, income eligibility operator, benefit formula, entity assignments, naming conventions, no hardcoded values

Needs Human Decision

• SSI in unearned income list: Regulations exempt SSI recipients (Sections 3.604.2.C.3.a, 3.605.3.D.27). This is pre-existing and should be addressed in a separate PR.
• 2013 grant standard values: 34 values sourced from an older CCR PDF (~2015 version) that may not be the exact 2013 regulation. Values are consistent with secondary sources but no 2013-era CCR PDF was found.
• 100% first certification period earned income disregard (eff. 6/1/2023): Not modeled due to PolicyEngine's single-period architecture.

Test Plan

• All existing tests pass (104 tests)
• New historical tests pass (2014 era)
• New 2024 era tests pass
• Edge case tests pass
• Microsimulation check (if applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (55a0045) to head (33a7306).
⚠️ Report is 15 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #7507      +/-   ##
===========================================
+ Coverage   97.82%   100.00%   +2.17%     
===========================================
  Files           3         2       -1     
  Lines          92        21      -71     
  Branches        2         0       -2     
===========================================
- Hits           90        21      -69     
+ Misses          1         0       -1     
+ Partials        1         0       -1     

Flag	Coverage Δ
unittests	100.00% <100.00%> (+2.17%)	⬆️

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