feat: Skip backtracking when far behind,Accept PubSub events after idle

[patriknw]

Since we had a stack of related PRs I incorporated them into one single PR. This includes

• https://github.com/akka/akka-persistence-r2dbc/pull/599
• https://github.com/akka/akka-persistence-r2dbc/pull/600
• https://github.com/akka/akka-persistence-r2dbc/pull/612
• https://github.com/akka/akka-persistence-r2dbc/pull/613