review: refactor: Controlflow cleanup

[Mr-Pine]

The control flow module is in dire need of a (spring) cleaning. As it is currently spring, this PR does at least some of the work, including:

• Moving to a better package name
• Removing unused and broken code
• Finding better replacements for single letter variables
• Move to modern java features such as enhanced switch expressions and type patterns
• Updating dependencies
• Fixing broken javadoc comments
• Replacing raw types

[MartinWitt]

Please use mvn com.mycila:license-maven-plugin:4.1:format for the headers.