REF: use datetime C API instead of getattrs
@WillAyd i think there are a couple of paths that must not be reached, since it looks like they pass np.datetime64 objects to these pydatetime-requiring functions.  in python/cython id check that with an `assert False`.  have a favorite way of doing that in c code?
it works locally, but im seeing build failures from the type checking Closing as not worth the trouble.