Generalising functions to support `GenericUnit` #764

Job	Run time
Julia 1 - ubuntu-latest -	33s
Julia lts - ubuntu-latest -	23s
Julia lts - macOS-latest -	30s
Julia lts - windows-latest -	1m 3s
Julia 1 - windows-latest -	1m 4s
Julia 1 - macOS-latest -	50s
Julia nightly - ${{ matrix.os }} - ${{ matrix.arch }}	0s
	4m 23s

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