Resolve EVM code outside of newComputation

[jangko]

From Discord chat:

#2881 reduces seq overhead in EVM - that said, @jangko the design where newComputation sometimes does database lookups feels pretty hairy - can't that be moved somewhere else? it feels like unnecessary maintenance overhead to do the same thing in two places
[20.23]
basically, for precompiles in particular, we don't execution evm opcodes so correspondingly we don't need a stack/memory - the natural way to solve that would be that the code is always resolved "outside" of newComputation and if code is nil, we skip stack/mem allocation instead of that ugly flag..

this also would help with the logic of reducing database lookups for precompiles - the database check is unnecessary (and expensive) - the PR introduces an ugly hack to fix this but ...