SNAP CBPP test and fixes

[MaxGhenis]

Recreating #375 because the version checker isn't working there

Fixes #1155
Fixes #1156

Adds SNAP integration tests from https://www.cbpp.org/research/food-assistance/a-quick-guide-to-snap-eligibility-and-benefits

Adds metadata for PolicyEngine

[MaxGhenis]

Filed #1158 on the version check failure

[codecov]

Codecov Report

Merging #1157 (a1d07fe) into master (0bdaa2d) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1157   +/-   ##
=======================================
  Coverage   95.36%   95.36%           
=======================================
  Files         733      733           
  Lines       13030    13031    +1     
  Branches      939      940    +1     
=======================================
+ Hits        12426    12427    +1     
  Misses        568      568           
  Partials       36       36           

Impacted Files	Coverage Δ
.../deductions/shelter/snap_net_income_pre_shelter.py	100.00% <100.00%> (ø)

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