Move coalesced logic from Unscheduled to Scheduled Write-Behind or asynchronous cache store

In the async cache store, remove coalescing of modifications from Unscheduled Write-Behind or strategy and move it to the Scheduled Write-Behind strategy.

The aim of the Unscheduled strategy is to be as fast as possible. Having to deal with coalescing changes is only going to slow it down for very little gain. Coalescing changes in an schedule strategy makes a lot more sense.