Implement pybind11-based CPU JIT compiler + basic testing.

mypy.ini

pyproject.toml

src/pystencils/backend/emission/base_printer.py

src/pystencils/backend/emission/c_printer.py

src/pystencils/jit/__init__.py

src/pystencils/jit/cpu/__init__.py

src/pystencils/jit/cpu/cpu_pybind11.py

src/pystencils/jit/cpu/kernel_module.tmpl.cpp

src/pystencils/sympyextensions/__init__.py

tests/jit/test_cpujit.py