fix: re-export the DecimalType for consumers

[rtyler]

This seems a reasonable thing to export.

Fixes #3279

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.37%. Comparing base (4036166) to head (7c4b7b8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3738   +/-   ##
=======================================
  Coverage   75.37%   75.37%           
=======================================
  Files         145      145           
  Lines       43946    43946           
  Branches    43946    43946           
=======================================
+ Hits        33123    33125    +2     
+ Misses       9219     9217    -2     
  Partials     1604     1604           

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