Implement unit conversion for contour levels #385

Job	Run time
initial_checks / Load tox environments	8s
initial_checks / codestyle (ubuntu-latest)	32s
no_coverage / Load tox environments	9s
tests / Load tox environments	4s
tests / py38-test (ubuntu-latest)	2m 6s
tests / py39-test (ubuntu-latest)	2m 5s
tests / py310-test (ubuntu-latest)	2m 38s
tests / py311-test (ubuntu-latest)	2m 17s
tests / py38-test (macos-latest)	3m 49s
tests / py39-test (macos-latest)	4m 17s
tests / py311-test (macos-latest)	4m 18s
tests / py38-test (windows-latest)	4m 10s
tests / py39-test (windows-latest)	3m 21s
tests / py310-test (windows-latest)	3m 47s
no_coverage / py39-notebooks (windows-latest)	3m 26s
no_coverage / py38-notebooks (macos-latest)	2m 12s
no_coverage / py310-notebooks (ubuntu-latest)	1m 36s
no_coverage / py311-docs (ubuntu-latest)	1m 30s
no_coverage / py39-docs (macos-latest)	1m 56s
no_coverage / py38-docs (windows-latest)	3m 11s
publish / Build source and wheel distribution	4m 47s
	52m 19s

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