Replace isAssignableFrom with == for final classes, refactor retrieveMethodAccessor

[snuyanzin]

For final classes isAssignableFrom could be replaced with == to avoid calling native methods

[codecov-commenter]

Codecov Report

Merging #440 (2b5d293) into main (8e86786) will increase coverage by 0.00%.
The diff coverage is 78.94%.

❗ Current head 2b5d293 differs from pull request most recent head 64df541. Consider uploading reports for the commit 64df541 to get more accurate results

@@            Coverage Diff            @@
##               main     #440   +/-   ##
=========================================
  Coverage     93.95%   93.95%           
+ Complexity     2003     2001    -2     
=========================================
  Files           222      222           
  Lines          4017     4019    +2     
  Branches        384      382    -2     
=========================================
+ Hits           3774     3776    +2     
  Misses          146      146           
  Partials         97       97           

Impacted Files	Coverage Δ
.../java/net/datafaker/service/FakeValuesService.java	87.25% <78.94%> (+0.05%)	⬆️

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