additional tests & some fixes

src/pystencils/nbackend/kernelcreation/freeze.py

src/pystencils/nbackend/kernelcreation/typification.py

src/pystencils/nbackend/types/__init__.py

src/pystencils/nbackend/types/basic_types.py

src/pystencils/nbackend/types/parsing.py

src/pystencils/nbackend/types/quick.py

tests/nbackend/test_cpujit.py

tests/nbackend/test_types.py

tests/nbackend/test_typification.py