Problem/Motivation
This is a follow-up to #2500521: Upgrade path for Statistics 7.x and 6.x where we identified that StatisticsViewsResult was (sometimes) returning strings when it should only ever return integers.
Proposed resolution
Cast the inputs to integer in the constructor.
Remaining tasks
Write patch.
Review patch.
etc.
Removes @todo from Drupal\Tests\statistics\Kernel\Migrate\d6\MigrateNodeCounterTest and Drupal\Tests\statistics\Kernel\Migrate\d7\MigrateNodeCounterTest (assuming #2500521: Upgrade path for Statistics 7.x and 6.x lands first).