This PR amends the way Leafs of Merkle trie with even paths are stored, so that if the path starts with a nibble in form of 0b11__ it will be one byte shorter to store. As 0b11 is a one of four prefixes, with a uniform distribution 1/4 of even paths should require one byte less to store.

The optimization uses the fact that Type.Leaf is encoded in first byte as 0b1000_0000. This plus the fact that other higher bits are not used by other cases, allows to use 0b11 as a discriminator of a leaf that has some property. In that case it's the property that the path starts with 0b11 which allows us to not store any additional data beside the leaf's NibblePath. The leaf type is encoded in the path itself.

Benchmark

Importing Sepolia db.

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