Upgrade gradle and plugin version for library and sample app

[joshafeinberg]

Additionally added a sample test to confirm that assembleAffectedAndroidTests works properly in the sample

[codecov]

Codecov Report

Merging #127 (b6ca66c) into main (ceaf57a) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               main     #127   +/-   ##
=========================================
  Coverage     50.10%   50.10%           
  Complexity       59       59           
=========================================
  Files            12       12           
  Lines           455      455           
  Branches         94       94           
=========================================
  Hits            228      228           
  Misses          200      200           
  Partials         27       27           

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