Make cuda.core pass mypy test

[oleksandr-pavlyk]

With cuda.bindings and cuda.core installed locally:

(dev-cuda-python) opavlyk@ee09c48-lcedt:~/repos/cuda-python/cuda_core$ mypy tests | grep Found 
Found 160 errors in 19 files (checked 17 source files)

[leofang]

xref: #312, #505, #527