rlpToMerkleNode should be static

[no2chem]

Currently, it seems that rlpToMerkleNode needs to have an instance of a merkle tree. Does it actually need any fields of the Merkle tree to work? It seems it shouldn't, so it should either be static, or just an exported function

[SoujanyaPonnapalli]

rlpToMerkleNode : (rlpEncodedNode: Buffer) => MerklePatriciaTreeNode<V>
references the CachedMerklePatriciaTree class parameter V.

If rlpToMerkleNode is static, we will not be able to return a MerklePatriciaTreeNode<V>. We might have to return a generic MerklePatriciaTreeNode<any>.