Resolve "Make BaseDataContainer.__init__ non-abstract"

What does this MR do?

This MR takes care of #61 (closed) and, alongside that, improves modularisation of the mixins submodule.

Can this MR be accepted?

• Implemented the changes
• Tests added or adjusted
• Pipeline passes
• Changelog entry added

Anything to double-check?

Nope.

Related issues

Closes #61 (closed)