Renovation of the TestCase generation

[wadoon]

Intended Change

Make test case generation usable again, especially, from the CLI in the new verification template.

Type of pull request

• X Refactoring (behaviour should not change or only minimally change)
• X New feature (non-breaking change which adds functionality)
• X Breaking change (fix or feature that would cause existing functionality to change)
• X There are changes to the (Java) code
• X Renovations

Changes

• Use of JavaPoet for the generation of valid Java code. Nobody understands pages of StringBuilder foo.
• Facade
• Clean up of old Java (introduction of records, sealed hierarchies, NPE checking, ...)