Pass only LO words of wrapping proof inputs

[dtebbs]

Inputs to the wrapper proof are currently passed as bw6-761 scalars (2 evm words) but can be held in a single evm word and zero padded only when required for proof verification.
The same is true for hashes (vk and inputs) is they do not exceed 256 bits.

UPDATE: most Inputs to the wrapper proof are passed to the contract as bw6-761 scalars (2 evm words) but can be held in a single evm word and zero padded when required for proof verification. One exception is the nested vk hash (#67), which requires a full (2-word) scalar.