Introduce a SafeFraction that carefully handles operations on Fraction instances

[uhafner]

Otherwise the Fraction class will produce an overflow and throws an ArithmeticException.

[codecov]

Codecov Report

Merging #415 (ad2fcf1) into master (02ba219) will increase coverage by 0.14%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #415      +/-   ##
============================================
+ Coverage     71.45%   71.60%   +0.14%     
- Complexity      980      984       +4     
============================================
  Files            86       87       +1     
  Lines          3713     3722       +9     
  Branches        436      436              
============================================
+ Hits           2653     2665      +12     
+ Misses          914      911       -3     
  Partials        146      146              

Impacted Files	Coverage Δ
...o/jenkins/plugins/coverage/model/CoverageNode.java	94.34% <100.00%> (+1.18%)	⬆️
...ins/plugins/coverage/model/CoveragePercentage.java	86.48% <100.00%> (+0.37%)	⬆️
...o/jenkins/plugins/coverage/model/SafeFraction.java	100.00% <100.00%> (ø)

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