feat(Mamba): Remove code related to Mamba

[rrutmann]

What does this PR do?

This PR removes all code related to Mamba. The latest state of main with Mamba can be found in the branch main_with_mamba.

General Changes

• Removes Mamba-related code

Breaking Changes

• None

Checklist before submitting final PR

• [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)