Fixes #542: Now using `::cuda::` or sub-namespaces as appropriate in … #523

Job	Run time
build (windows-2019, 12.1.1, Visual Studio 16 2019, powershell, windows, -A x64)	18m 37s
build (windows-2019, 12.0.1, Visual Studio 16 2019, powershell, windows, -A x64)	17m 44s
build (windows-2019, 11.8.0, Visual Studio 16 2019, powershell, windows, -A x64)	17m 56s
build (windows-2019, 11.7.0, Visual Studio 16 2019, powershell, windows, -A x64)	13m 16s
build (windows-2019, 11.6.2, Visual Studio 16 2019, powershell, windows, -A x64)	15m 51s
build (windows-2019, 11.6.1, Visual Studio 16 2019, powershell, windows, -A x64)	9m 27s
build (windows-2019, 11.6.0, Visual Studio 16 2019, powershell, windows, -A x64)	8m 35s
build (windows-2019, 11.5.0, Visual Studio 16 2019, powershell, windows, -A x64)	10m 57s
build (windows-2019, 11.4.0, Visual Studio 16 2019, powershell, windows, -A x64)	8m 21s
build (windows-2019, 11.3.0, Visual Studio 16 2019, powershell, windows, -A x64)	9m 37s
build (windows-2019, 11.2.2, Visual Studio 16 2019, powershell, windows, -A x64)	9m 47s
build (windows-2019, 11.1.1, Visual Studio 16 2019, powershell, windows, -A x64)	8m 13s
build (windows-2019, 11.0.3, Visual Studio 16 2019, powershell, windows, -A x64)	8m 56s
	2h 37m 17s

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