Start on GPU extensions #681

Job	Run time
Julia lts - ubuntu-latest -	13m 6s
Julia 1 - ubuntu-latest -	16m 39s
Julia lts - windows-latest -	15m 34s
Julia 1 - macOS-latest -	15m 22s
Julia lts - macOS-latest -	11m 29s
Julia 1 - windows-latest -	17m 33s
Julia nightly - ${{ matrix.os }} - ${{ matrix.arch }}	-1s
	1h 29m 42s

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