Validate the loaded entry-point type at runtime using typeguard

[roeey777]

Currently the library can only assume adherence to the Plugin = Callable[[bytes], bytes] type annotation.
However this isn't good enough.

Definition of Done
Use typeguard from the embedded python code in the C++ in order to enfoce compliance with our Plugin type annotation.
In addition, by adding typeguard one should also add a Requires-Dist: typeguard>=[minimal version],<[maximal version] to the installed METADATA file.
Maybe it would be better if the installed python package would be managed seperatly using pyproject.toml and cmake would invoke pip install . somehow instead of installing all those .dist-info files.