Interface + base class structure for callback module

[GiovanniCanali]

Description

This PR fixes #800

In this PR, the following updates for the callback module have been introduced:

• Renamed NormalizerDataCallback to DataNormalizer to align with PINA conventions.
• Added deprecation warnings for backward compatibility.
• Implemented the interface + base class structure for refinement callbacks.
• Enhanced and extended documentation to improve clarity and usability.
• Enhanced test suite to improve coverage.

The core logic underpinning the entire callback module has remained unchanged from a user perspective.

Checklist

• Code follows the project’s Code Style Guidelines
• Tests have been added or updated
• Documentation has been updated if necessary
• Pull request is linked to an open issue

[GiovanniCanali]

Currently on hold, waiting for #801 to be merged.