CI: micromamba and environment caching #278

Job	Run time
mypy	2m 53s
py3.12 \| macos \| integration tests	12m 48s
py3.12 \| macos \| unit tests	9m 47s
py3.12 \| ubuntu \| integration tests	16m 50s
py3.12 \| ubuntu \| unit tests	12m 29s
py3.12 \| windows \| integration tests	30m 11s
py3.12 \| windows \| unit tests	19m 32s
py3.10 \| ubuntu \| unit tests	11m 34s
py3.11 \| ubuntu \| unit tests	11m 26s
merge-test-artifacts	0s
	2h 7m 30s

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