Implement a transaction queue

[carneiro-cw]

This not only enables queueing ordered transactions by their nonce, but could enable us to perform optimizations when transactions are in the queue before they begin execution. Some possible ideas:

• Loading slots to cache by running eth_call while they are queued
• Dependency graph by observing which slots/accounts they read/write, enabling parallel transaction execution
• Rejecting invalid transactions before they start executing (subsequently blocking other transactions from executing)