Return `DecodedMultiProof` from multiproof threads

[Rjected]

Right now we return a MultiProof from multiproof threads:

reth/crates/engine/tree/src/tree/root.rs

Line 424 in b955551

multiproof: proof,

This contains ProofNodes which then needs to be decoded in reveal_multiproof. This can take up to 8-10% of time in the critical path.

This 8.6% is this line:

reth/crates/trie/sparse/src/state.rs

Line 251 in b955551

let node = TrieNode::decode(&mut &bytes[..])?;

Instead, we should do this before returning a multiproof response. This involves creating a new struct DecodedProofNodes, creating Decoded versions of proof structs, and using them in the sparse trie instead of the non-decoded versions we have right now.