Update documentation and docstrings for DataProcessors

[MooooCat]

Description

This PR updates the documentation and docstrings for the DataProcessors. The changes include:

1. Adding a detailed description of the class and its methods to the class docstring.
2. Updating the documentation in the index.rst file to reflect the changes.

Motivation and Context

he current docstring and documentation are not detailed enough, which makes it difficult for new users to understand how to use DataProcessor. This PR aims to improve the clarity and usability of these classes.

How has this been tested?

We use make html to build the documentation locally to ensure formatting and links are correct.

Types of changes

• [x] Maintenance (no change in code, maintain the project's CI, docs, etc.)
• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.

[iokk3732]

done