added ruff for import sorting of generated code

[haeussma]

Refactored preservation of custom code upon code generation

Updated general strategy

• previous code is dissected into strings, representing:
  • imports
  • globals
  • sdrdm-generated code
  • custom methods
• imports of new and previous code are combined using ast
• individual strings are combined, and the changes from the updated generated code added to the previous file

Changes:

• Imports are now sorted using isort, provided by ruff
• added support to detect async function definitions
• added detection of generated validator patterns