Core: Better holders

[iopapamanoglou]

Core: Better holders

Description

Very much work in progress!
Another step towards bringing faebryk from ASM to C in terms of usability.

This will most likely result in faebryk 4.0.0

Checklist

Please read and execute the following:

• My code follows the coding guidelines of this project
• My PR title is following the contribution guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (if applicable)
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works (if applicable)
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I ran Black to format my code

Code of Conduct

By submitting this issue, you agree to follow our Code of Conduct:

• I agree to follow this project's Code of Conduct