Stateless: Create ExecutionWitness type and implement encoding/decoding

[bhartnett]

This ExecutionWitness type follows the structure used by Ress and also Geth, see here:
https://github.com/ethereum/go-ethereum/blob/bc67e7dd487189b828d63927b453f4af2e67f2ff/core/stateless/witness.go#L38
https://docs.rs/alloy-rpc-types-debug/latest/alloy_rpc_types_debug/struct.ExecutionWitness.html

Here is write up on the topic from the Geth team: https://gist.github.com/karalabe/47c906f0ab4fdc5b8b791b74f084e5f9

This structure is different to the prior block witness structure used and this version is actually much simpler to understand and implement. The state is simply a list of MPT nodes (both account and storage tries together). The codes field is the list of bytecodes used/executed by the block. The keys is the ordered list of addresses or storage slot keys accessed while executing the block and the headers contains the list of headers required to prove that the witness is correct. Before the recent Prague hardfork this would have contained all the headers required to support the BLOCKHASH opcode but now since this opcode is implemented using a system contract this field should only need to contain the parent header which is required to validate the witness against the parent state root before starting stateless execution.

This ExecutionWitness type will also be used to implement the debug_executionWitness and debug_executionWitnessByBlockHash RPC endpoints.