op-program: reuse EVM instance in L2 block processor

[protolambda]

See AddTx:

optimism/op-program/client/l2/engineapi/block_processor.go

Line 135 in d39eb24

func (b *BlockProcessor) AddTx(tx *types.Transaction) error {

The intermediate geth v1.14.12 -> v1.14.13 changes (see PR #13958) allow for easy EVM-instance reuse between txs of the same block.

This was left unoptimized out of caution, but can be changed. Specifically, the mkEVM() can be called once (and provider.GetVMConfig() usage can be simplified) in NewBlockProcessorFromHeader, and the *vm.EVM instance can then be shared between txs.