Add `fee` to transaction

[leonardoalt]

By signing the tx, the user agrees that the fee will be subtracted from their account and given to the block.coinbase at the end of the transaction.

Tasks:

• [ ] Add fee to the Tx types in the subcrates
• [ ] Create an L2 block type that has a list of transactions and a coinbase
• [ ] Modify L1 verifier contract to take in the new block instead of txs
• [ ] Modify sequencer to send block (with its own public key as the coinbase) instead of txs
• [ ] Add tx.fee and block.coinbase to the circuit which also adds the fee transfer to the state update