Deserialize for array groups with optional fields

[rooooooooob]

Fixes #203

Fixes #154 as this issue popped up while making sure optional fields were very well supported.

[rooooooooob]

TODO: add test for preserve-encodings=true

Edit: Done

[rooooooooob]

This will also be useful for when we generate conway.cddl. And any time regenerating things from alonzo/babbage without needing to hand-edit the optional field for the tx outputs.

[SebastienGllmt]

Can we be sure to update the docs if relevant when we add new features?

[gostkin]

looks like one test is failing:

test test::rust_wasm_split ... FAILED

[rooooooooob]

@gostkin the test is failing on master it seems too. I fixed it in #207

[rooooooooob]

@SebastienGllmt I don't think the docs need changing, at least in its current format. We still don't support deserialization for 100% of types, although it is much, much better now, so I think the current statement of * Deserialization for almost all supported types is fine. Only more ambiguous array types aren't supported now so most real-world cddls written to have parsing logic not a pain to write should be fine. I thought we are using issues for unsupported things not the docs?