Split Commitments for structs

[lydiagarms]

Currently starlight does not support split commitment for structs.

The main hurdle currently is that the splitCommitments.zok circuit cannot handle structs. The value input (which is the value of the commitment that needs to be split) is a field, but we need it to be a struct.

The solution would be for every struct defined in the contract to create a new splitCommitment circuit. For example if we have the structs defined struct1, struct2, struct3 we would need splitCommitmentsstruct1.zok, splitCommitmentsstruct3.zok, splitCommitmentsstruct3.zok.

Also look into whether we can do the same for joinCommitments. This is complicated by the fact we need to check whether the amount in a struct is high enough for every property.