Adapt SFG to field typing changes in pystencils

...urce/usage/examples/guide_generator_scripts/05/kernels.py

src/pystencilssfg/lang/cpp/std_mdspan.py

src/pystencilssfg/lang/cpp/std_span.py

src/pystencilssfg/lang/cpp/std_vector.py

src/pystencilssfg/lang/cpp/sycl_accessor.py

tests/lang/test_cpp_stl_classes.py