Measure and track `cuda.core` import time

[leofang]

It is a good indicator because it also covers cuda-bindings and cuda-pathfinder.

[mdboom]

Maybe @danielfrg would be interested in adding this to the benchmarking suite?

It would be good to (1) exclude time spent getting to basic Python (python -c pass time), and also measure "time to calling first driver.init()", because that includes not just Python import, but dlopen-ing and then resolving all the symbols.

[mdboom]

Should merge this #2005 first before starting on this -- it would be helpful to have a cuda_core benchmark suite first.