Mark ccp module and test standalone

Author: schnellerhase

.github/workflows/ccpp.yml

@@ -145,6 +145,7 @@ jobs:
           . ./mypy-env/bin/activate
           pip install mypy types-cffi scipy-stubs
           mypy -p dolfinx
+          mypy -p dolfinx.cpp
         # mypy test
         # mypy demo
 

python/CMakeLists.txt

@@ -195,6 +195,7 @@ nanobind_add_stub(
   RECURSIVE
   INSTALL_TIME
   OUTPUT_PATH dolfinx
+  MARKER_FILE dolfinx/cpp/py.typed
   OUTPUT
     dolfinx/cpp/fem/__init__.pyi
     dolfinx/cpp/fem/petsc.pyi