Switch from os.path to pathlib in MeshCat visualizer #123

Job	Run time
ubuntu-latest - Env all Release	40m 6s
ubuntu-latest - Env all Debug	39m 29s
ubuntu-latest - Env all-py39 Release	39m 47s
ubuntu-latest - Env all-py39 Debug	40m 9s
macos-latest - Env all Release	1m 36s
macos-latest - Env all Debug	19m 52s
macos-latest - Env all-py39 Release	23m 22s
macos-latest - Env all-py39 Debug	18m 33s
macos-13 - Env all Release	4m 33s
macos-13 - Env all Debug	38m 58s
macos-13 - Env all-py39 Release	46m 6s
macos-13 - Env all-py39 Debug	41m 40s
windows-latest - Env all Release	1h 16m 8s
windows-latest - Env all-clang-cl Release	7m 44s
check-macos-linux-windows-pixi	3s
	7h 18m 6s

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