Make `rlp_node` take `rlp_buf` as mutable argument

[Rjected]

Describe the feature

Right now we use the RevealedSparseTrie's rlp_buf field whenever we call rlp_node:

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

Line 1028 in b15c1c8

self.rlp_buf.clear();

This should instead be an argument that's passed as &mut, this way we can have one per thread

Additional context

No response

[nadtech-hub]

Can you assign it to me?