Type revision

[mpetrunic]

Since my attempt to improve types just scratched surface, I would suggest some bottom to top type revision

I would like to confirm some basic presumptions:

type BasicValue = bigint | number | boolean | Uint8Array:

type CompositeValue = Record<string, unknown> | ArrayLike<BasicValue | CompositeValue> | {}; // last one is hack for eth2 type interfaces to work. We could maybe just add it to Container generic?

[mpetrunic]

cc @wemeetagain Please write down other predicates that must be respected for other ssz primitives.