python3.withPackages: don't propagate build dependencies

[SomeoneSerge]

Issue description

Native extensions for python often can be used both as python packages and as shared libraries, e.g. consumable via CMake's find_package. Sometimes the *Config.cmake modules (&c) generated by these projects cannot be consumed without manually providing their transitive dependencies again. In these cases we simplify the setup using nix-support/propagated-build-inputs.

Currently, however, python3Packages use propagatedBuildInputs to specify the (python) runtime dependencies, which get written into the same ${!outputDev}/nix/propagated-build-inputs as the build-time native dependencies would. This sometimes forces us to bring entire toolchains (e.g. nvcc and the huge static libraries in case of cuda) into the runtime closures of python3.withPackages instances, increasing closures sizes and the frequency of rebuilds.

Related: #272179

• python3Packages.torch: cudaPackages.setupCudaHook: propagate deps and the hook #271078, uses a custom cxxdev output which should be eventually deleted
• python3Packages.opencv4: 7954fc6, cxxdev
• python3Packages.vtk: vtk: switch to vtk_9 #178367 (comment) (vtk_9: propagate libX11 and libGL on Linux #206935), ${!outputDev}