Start on GPU extensions #694

Job	Run time
Julia 1 - windows-latest -	17m 36s
Julia 1 - ubuntu-latest -	16m 9s
Julia lts - macOS-latest -	12m 20s
Julia lts - ubuntu-latest -	12m 42s
Julia 1 - macOS-latest -	13m 36s
Julia lts - windows-latest -	14m 33s
Julia nightly - ${{ matrix.os }} - ${{ matrix.arch }}	-1s
	1h 26m 55s

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