This PR introduces a new debug feature, logging the slow blocks with
detailed performance statistics, such as state read, EVM execution and
so on.
Notably, the detailed performance statistics of slow blocks won't be
logged during the sync to not overwhelm users. Specifically, the statistics
are only logged if there is a single block processed.
Example output
```
########## SLOW BLOCK #########
Block: 23537063 (0xa7f878611c2dd27f245fc41107d12ebcf06b4e289f1d6acf44d49a169554ee09) txs: 248, mgasps: 202.99
EVM execution: 63.295ms
Validation: 1.130ms
Account read: 6.634ms(648)
Storage read: 17.391ms(1434)
State hash: 6.722ms
DB commit: 3.260ms
Block write: 1.954ms
Total: 99.094ms
State read cache: account (hit: 622, miss: 26), storage (hit: 1325, miss: 109)
##############################
```
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