Speed up account ledger a little

[arnetheduck]

persist is a hotspot when processing blocks because it is run at least once per transaction and loops over the entire account cache every time.

Here, we introduce an extra dirty map that keeps track of all accounts that need checking during persist which fixes the immediate inefficiency, though probably this could benefit from a more thorough review - we also get rid of the unused clearCache flag - we start with a fresh cache on every fresh vmState.

• avoid unnecessary code hash comparisons
• avoid unnecessary copies when iterating
• use EMPTY_CODE_HASH throughout for code hash comparison

[jangko]

Improvement on my machine:

• Windows:
  • test_generalstate_json from 2m15s become 1m56s
• WSL Linux:
  • test_generalstate_json from 2m10s become 2m6s

A real linux machine should be faster. But this already set a new record. It never went below 2 minutes before on my machine.

[arnetheduck]

test_generalstate_json from 2m15s become 1m56s

interesting - I would not have expected it to matter on the general state tests since they're mostly small ..