increase diversifier size to 16 byte

[redshiftzero]

In #430 we added jumbled address encoding. As part of that change, we added a five byte padding (such that the f4jumble construction operates on 16 byte blocks). However, this means there is wasted space in our addresses.

This change is to:

• remove the 5 bytes of padding in the address encoding/decoding prior to running through f4jumble
• increase the size of the diversifier field from 11 to 16 bytes (making it a u128)

⚠️: this is a breaking change to addresses and should be coordinated with the other incoming changes that break the address format