stats: optimism `new_contracts` bug

[bragov4ik]

Issue https://github.com/blockscout/blockscout-rs/issues/841 follows from inaccurate data in chart new_contracts.

Possible reasons and

Apparently, blockscout reindexes old transactions, which is not considered for chart updating.

Fix directions

Changing logic of the update should help. In particular, utilizing field updated_at in table transactions with the help of corresponding index. I.e. query txn's added after last sync and add the result to stats DB.

Note: need to consider updates that do not result in changing created_contract_address_hash field. How - not sure rn. Maybe just recalculate data for days where update was observed.

[bragov4ik]

related, but seems more general: https://github.com/blockscout/blockscout-rs/issues/514