explore the possibility of unify process_transaction and tx_packer

[jangko]

Both process_transaction.nim and tx_packer.nim share a lot of similarities: executing a transaction.
Although they now have differences, maybe we can somehow unify both of them similar to what we have done with various emv call in the past.

The new EIP-1153 and old one like EIP-158/161 proves having two transaction execution increase maintenance cost because we have to modify code in two places rather than only in one place.

tx_packer is less tested compared to process_transaction hence may lead to regression without we being aware of it.