Change the raw signature values to use `TransactionSignature`

[manuelmauro]

cc @manuelmauro: polkadot-evm/frontier#1700

We need to change the raw signature values to use TransactionSignature instead. Otherwise it won't properly verify EIP-2.

Originally posted by @sorpaas in #63 (comment)

[manuelmauro]

Addressed in 2dd9d1d