Nullability is broken by move to reference schemas

[brizzbuzz]

Describe the bug
The switch to reference schemas completely broken Kompendiums ability to handle null fields. Since each type gets stored only once, but nullability is stored on the object schema level, this leads to a situation where defining one field of Type A that is nullable and another field of type A that is not nullable cannot be handled.

To Reproduce

data class Something(val a: String, val b: Int)

data class ManyThings(
  val someA: Something,
  val someB: Something?
)

This will not display the nullability correctly in Kompendium

Expected behavior
It should display properly

[brizzbuzz]

Read through this at some point OAI/OpenAPI-Specification#1368