[fix] add module for backward compatibility

cache_property has been added in py3.8 [1]

To support cache_property in py3.7 the implementation from 3.8 has been
copied to compat.py.  This code can be cleanup with EOL of py3.7.

[1] https://docs.python.org/3/library/functools.html#functools.cached_property



Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>