Fixing bug identified in Ticket #60055 where metrics related to FileIO were no longer being sent as Deltas. It looks like this was mistakenly broken while trying to fix the RecompileSummary (https://github.com/newrelic-platform/newrelic_microsoft_sqlserver_plugin/commit/dd0a651ed6050cc5f27780adbfab0f1820b27b49).

Added a test to make sure we don't face this regression issue again.