Introduce visp namespace to protect ViSP classes #1920

Job	Run time
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/gcc-9, /usr/bin/g++-9, 98)	1m 52s
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/gcc-9, /usr/bin/g++-9, 11)	15m 25s
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/gcc-9, /usr/bin/g++-9, 17)	16m 56s
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/gcc-10, /usr/bin/g++-10, 98)	2m 7s
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/gcc-10, /usr/bin/g++-10, 11)	13m 43s
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/gcc-10, /usr/bin/g++-10, 17)	14m 55s
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/clang, /usr/bin/clang++, 98)	2m 0s
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/clang, /usr/bin/clang++, 11)	17m 3s
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/clang, /usr/bin/clang++, 17)	16m 56s
build-ubuntu-dep-apt (ubuntu-22.04, /usr/bin/gcc-9, /usr/bin/g++-9, 98)	1m 36s
build-ubuntu-dep-apt (ubuntu-22.04, /usr/bin/gcc-9, /usr/bin/g++-9, 11)	10m 16s
build-ubuntu-dep-apt (ubuntu-22.04, /usr/bin/gcc-9, /usr/bin/g++-9, 17)	9m 30s
build-ubuntu-dep-apt (ubuntu-22.04, /usr/bin/gcc-10, /usr/bin/g++-10, 98)	1m 47s
build-ubuntu-dep-apt (ubuntu-22.04, /usr/bin/gcc-10, /usr/bin/g++-10, 11)	9m 7s
build-ubuntu-dep-apt (ubuntu-22.04, /usr/bin/gcc-10, /usr/bin/g++-10, 17)	8m 0s
build-ubuntu-dep-apt (ubuntu-22.04, /usr/bin/clang, /usr/bin/clang++, 98)	1m 52s
build-ubuntu-dep-apt (ubuntu-22.04, /usr/bin/clang, /usr/bin/clang++, 11)	3m 12s
build-ubuntu-dep-apt (ubuntu-22.04, /usr/bin/clang, /usr/bin/clang++, 17)	14m 40s
	2h 40m 57s

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