CI: micromamba and environment caching #279

Job	Run time
mypy	2m 6s
py3.12 \| macos \| integration tests	11m 39s
py3.12 \| macos \| unit tests	8m 31s
py3.12 \| ubuntu \| integration tests	16m 24s
py3.12 \| ubuntu \| unit tests	11m 59s
py3.12 \| windows \| integration tests	30m 6s
py3.12 \| windows \| unit tests	20m 1s
py3.10 \| ubuntu \| unit tests	10m 52s
py3.11 \| ubuntu \| unit tests	11m 7s
merge-test-artifacts	0s
	2h 2m 45s

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