What does this PR do?

This PR adds docstrings to all model related modules, enhancing code documentation and readability.

General Changes

[x] My PR is minimal and addresses one issue in isolation
[x] I have merged the latest version of the target branch into this feature branch
[x] I have reviewed my own code w.r.t. correct implementation, missing type hints, proper documentation, etc.
[x] I have run a sample config for model training
[x] I have checked that all tests run through (python tests/tests.py)
[x] I have updated the internal changelog (CHANGELOG_DEV.md)