dont allow nested objects that are not DomainObjects, use this knowledge to require DomainObject.nested is set when using serialize or getUniqueIdentifier

[uladkasach]

if we do this, then we will guarantee that user can not use serialize or getUniqueProperties dangerously even without the linter specified in #7

this may also just be a good constraint to enforce on people in general. I.e., flatten your keys - or define a DomainObject for the thing you're bundling.

[uladkasach]

we went as far as we could with this, by just throwing an error if the object having manipulation on it is either:

• not a domain object
• not a safe domain object (i.e., has nested, not specified objects at all)

we will not require users to define nested every time though - as they could easily just say they dont want to support serialize and getUniqueIdentifier