[shutter] integration tests

[taratorio]

capture entirety of block building with shutter enabled in an integration test:

• start an instance of eth.Ethereum
• use in-memory go libp2p hosts to simulate exchange of decryption keys
• submit transactions via existing erigon rpc for devp2p pool
• submit encrypted transactions to sequencer contract (construct them in test harness and submit via existing erigon rpc)
• submit transactions via rpc that simulate changes to eon key
• build a block - cover cases where there is only shutter transactions in a block (check encrypted pool gas limit), a mix of shutter and devp2p transactions (shutter ones must be on top of the block), no decryption keys received in time for validator (block must be empty), etc.