improve log puller

[lidezhu]

This is a collection for log puller improvement, including fix bugs, improve performance, improve metrics & logs.

[lidezhu]

• fix unnecessary resolve lock task #4241
• Some regions failed to be deregistered after unregistering the subscription #4217
• add a metrics to track region incremental scan progress #4239
• Unsubscribe stop task doesn't propagate filterLoop in BDR mode #4261