txpool: add SetCode transactions to legacy pool

[colinlyguo]

This PR adds SetCode transactions to the legacy pool.

rationale: although EIP-7702 introduces a new scenario where the EOA nonce can be incremented, it looks like the transaction pool can still handle addresses with updated nonces by monitoring newly added blocks on the node. This ensures that the nonce of transactions in the transaction pool will not be lower than the account's nonce. So, no changes are needed to the transaction pool's logic.

[lightclient]

We don't plan on enabling 7702 in the pool until a proper implementation is done. Thanks!

[colinlyguo]

We don't plan on enabling 7702 in the pool until a proper implementation is done. Thanks!

oh got it. thanks for the clarification. so the missing pieces are on purpose for version control.

[colinlyguo]

We don't plan on enabling 7702 in the pool until a proper implementation is done. Thanks!

oh got it. thanks for the clarification. so the missing pieces are on purpose for version control.

also, as a complement for this pr, I realized enabling SetCode tx without tx pool logic change might not be enough after seeing this: https://eips.ethereum.org/EIPS/eip-7702#transaction-propagation, quote:

This is due to the fact that once an EOA has delegated to code, that code can be called by anyone at any point in a transaction. It becomes impossible to know if the balance of the account has been sweeped in a static manner.

also added an obvious missing commit in this comment: colinlyguo@09d7184