* Add a simple metric for statements out-of-view
* Avoid repeated out-of-view peer reputation change messages
* Log reporting status
* Address review comments
* Use counter to store a number of unexpected messages from a peer
* Distinguish different unexpected statements in the metrics
* Fix labels cardinality
* Rename metric name to `statements_unexpected`
* Move metrics to a separate unit, avoid unnecessary enum
* Prefer specific methods in lieu of public constants