Remove nullability from all iceoryx constructs

## Brief feature description

To reduce the likely-hood of bugs we should remove the null ability from constructs like:
- [ ] SmartChunk
- [ ] Sample
- [ ] Request
- [ ] Response
- [ ] SharedChunk

Furthermore, we should explicitly allow the relative and relocatable pointer to be nullable. Those are such low level constructs and on those layers `nullptr` maybe transports some information as well which would lead to unexpected surprises when raw pointer are suddenly no longer nullable.

Start by locating the definitions and tests for SmartChunk, Sample, Request, Response, SharedChunk, and the relative and relocatable pointers. Determine how nullability is currently represented, then verify that the listed constructs reject null while the pointer types explicitly continue to permit it.

Written by the indexing model from the issue text.