* Repeat log catch-up until it's close to the latest height.
* Add an oneshot channel to send catch up end complete.
* Fix comments.
* Fix tests.
* Fix ut.
* Change default concurrent sync threads
* enhance log level in sync store
* Add rwlock in sync store to avoid concurrency issue
* enhance serial sync state machine log level
* wrap Instant for debug purpose
* add timestamp for connecting peers state
* Select random peer to sync chunks
* return sync peers states instead of connected peers only
* Use tokio async RwLock for sync store