Separate call for loading code size from database
In the [current version](https://github.com/status-im/nimbus-eth1/blob/bda760f41dac22f66c9a3ffa56d25bd2f274f4d1/nimbus/db/ledger/accounts_ledger.nim#L420), code size requests load the full code instead of just the size.

Using `EXTCODESIZE` in contracts is cheap gasfee-wise - this can be used to increase memory usage of the client by loading lots of code that later doesn't get used.
