fix: update Coin to fix amount calculation issues

[forcodedancing]

Description

The Plus/Minus functions do not handle amount calculation correctly for some special cases. This pr will add safePlus safeMinus helper functions to handle the issue.

Rational

Fix amount calculation issues.

Examples

NA

[codecov-commenter]

Codecov Report

Merging #323 (0ed0109) into develop (28669c3) will increase coverage by 0.02%.
The diff coverage is 100.00%.

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Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #323      +/-   ##
===========================================
+ Coverage    46.42%   46.45%   +0.02%     
===========================================
  Files          242      242              
  Lines        23221    23231      +10     
===========================================
+ Hits         10781    10791      +10     
  Misses       11793    11793              
  Partials       647      647