cuda+py: swap out `imp` for `importlib` #31

Job	Run time
cmake-ci (windows-2022, llvm, Ninja, Release, ON)	3m 45s
cmake-ci (ubuntu-22.04, llvm, Ninja, Release, ON)	3m 48s
cmake-ci (ubuntu-22.04, gcc, Ninja, Release, ON)	3m 6s
cmake-ci (macos-12, llvm, Ninja, Release, ON)	2m 56s
cmake-ci (macos-12, gcc, Ninja, Release, ON)	1m 39s
cmake-ci (windows-2022, msvc, Ninja, Release, OFF)	3m 0s
	18m 14s

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