Simplify `get_offset_value_reference` and add unit tests

[tcoratger]

Simplify get_offset_value_reference and add unit tests

Description

• The logical test on base_addr and offset to know if we should return null is implicitly already provided by the Relocatable addition in the last step of the get_offset_value_reference function, so that I don't think it's needed is as an overhead.
• Two unit tests are added to test edge configurations.

Description of the pull request changes and motivation.

Checklist

• [ ] Linked to Github Issue
• [X] Unit tests added
• [ ] Integration tests added.
• [ ] This change requires new documentation.
  • [ ] Documentation has been added/updated.
  • [ ] CHANGELOG has been updated.