Measure performance with only 2 account header leaves instead of 5

[gballet]

In verkle trees, the account header consists of 5 leaves (version, balance, nonce, code keccak and code size), each of which takes 32 bytes. This means that calculating the commitment of a value costs at least 10 exponentiations (each value is split in 2 16-bytes value). Most of these values do not require 32 bytes (version, nonce, code size, let alone balance), and it would therefore be possible to pack some of them into a single 32-byte value in order to save on exponentiation costs.

[gballet]

Haven't done it yet, but it is unlikely to improve anything: given the structure of a LEafNode, most values end up being 0s. Grouping everything together will save space, but it will not save computation time as data is simply flushed around.

[gballet]

This is done as part of the Nyota update to the spec.