Use a versionned hash for the tree root

[gballet]

In order for rollups to use verkle trees, we are considering adding turning the root of the verkle tree into a versionned hash, so that it can be verified by the same (athough modified) precompile that is used in eip-4844.

The version number remains to be picked.

The first byte of the (pedersen hash of) the root commitment is replaced with the version number, and the dropped byte is added to the proof payload, for the precompile to be able to reconstruct the full tree from the proof.