fix: Fix rules for isbetween that was not validated.

[bvanelli]

Turns out isbetween does not share the model with any of the other of the the other entries, but rather implementes the the following data model:

{"num1": int1, "num2": int2}

This patch files this broken behaviour.

Closes #46

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.81%. Comparing base (c59a360) to head (126ad84).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #47      +/-   ##
==========================================
+ Coverage   96.77%   96.81%   +0.03%     
==========================================
  Files          13       13              
  Lines        1738     1758      +20     
==========================================
+ Hits         1682     1702      +20     
  Misses         56       56              

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