Migrate handler and syncer stats from `coreth`

[powerslider]

Summary

Migrate https://github.com/ava-labs/coreth/blob/master/sync/handlers/stats/stats.go and https://github.com/ava-labs/coreth/blob/master/sync/client/stats/stats.go to vms/evm/sync/stats package.