fix: zero value incorect comparison

[quagmt]

Issue

• Decimal value of zero obtained from subtraction does not equal to other zero values #10

Description

• Make zero value always udecimal.Zero to avoid unexpected result when comparing zero
  cc @mdawar

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.54%. Comparing base (9d5eef5) to head (634d488).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #12   +/-   ##
=======================================
  Coverage   94.53%   94.54%           
=======================================
  Files           5        5           
  Lines        1263     1265    +2     
=======================================
+ Hits         1194     1196    +2     
  Misses         37       37           
  Partials       32       32           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.