Add original PerTau and Milky Way 3D examples #273

Job	Run time
initial_checks / Load tox environments	7s
initial_checks / codestyle (ubuntu-latest)	22s
deploy-examples	0s
tests / Load tox environments	5s
tests / py39-test-all (ubuntu-latest)	3m 51s
tests / py310-test-all (ubuntu-latest)	3m 37s
tests / py311-test-all (ubuntu-latest)	3m 15s
tests / py312-test-all (ubuntu-latest)	3m 45s
tests / py312-test-qt (ubuntu-latest)	3m 10s
tests / py312-test-jupyter (ubuntu-latest)	2m 51s
tests / py39-test-all (macos-13)	20m 39s
tests / py310-test-all (macos-latest)	6m 25s
tests / py311-test-all (macos-latest)	4m 48s
tests / py312-test-all (macos-latest)	5m 44s
tests / py312-test-qt (macos-latest)	5m 12s
tests / py39-test-all (windows-latest)	5m 38s
tests / py310-test-all (windows-latest)	5m 30s
tests / py311-test-all (windows-latest)	6m 28s
tests / py312-test-all (windows-latest)	6m 46s
tests / py312-test-qt (windows-latest)	5m 30s
tests / py312-test-jupyter (windows-latest)	7m 1s
	1h 40m 44s

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