Don't store storage values twice

[jwasinger]

Currently, to make the implementation less invasive on the Geth codebase, storage values are stored twice:

• stored in the snapshot db, via the verkle trie which associates the storage value to its tree key: https://github.com/gballet/go-ethereum/blob/dca3c2e42a64119867a33ad1680763d8907f4f03/core/state/state_object.go#L375 . This is used for generating verkle proofs.
• stored in the snapshot db associated with the key used by non-verkle Geth: https://github.com/gballet/go-ethereum/blob/dca3c2e42a64119867a33ad1680763d8907f4f03/core/state/state_object.go#L385 . This is how Geth stores storage values pre-verkle.

It should be changed so that storage values are only stored once, each account's storage values are contiguous in the db, these values can be used to build the verkle proof (which will likely involve some metadata which maps the physical layout of storage values in the DB to their location in the suffix-tree level of the verkle tree.