Add test for checking CountsStore rotation

- expose total number of records written
- avoid returning a record if the count is zero
Rename CountStoreApplier to CountsStoreApplier
Avoid applying commands in recovery if they belongs to a transaction with id leq than the last tx id in the CountsStore
Add tests to CountsComputer
Remove old unnecessary test
Fix BatchingPageCache to use always a SYNCHRONOUS writer for the CountsStore

This is necessary to make sure that we write to disk immediately the changes to the
counts store since we circumvent the page cache to read the counts
Create a new CountsStore when migrating the stores from older versions