Start on GPU extensions #689

Job	Run time
Julia 1 - macOS-latest -	10m 52s
Julia lts - macOS-latest -	8m 30s
Julia 1 - windows-latest -	19m 14s
Julia lts - windows-latest -	14m 47s
Julia 1 - ubuntu-latest -	16m 37s
Julia lts - ubuntu-latest -	12m 57s
Julia nightly - ${{ matrix.os }} - ${{ matrix.arch }}	0s
	1h 22m 57s

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