Set up pixi for development #4458

Job	Run time
check-xarray-docs	13s
build-wheels	4m 32s
compat-stateful	1m 7s
xarray-backends (latest-release, latest-release, latest-release)	1m 28s
xarray-backends (minimum, 2025.07.1, 3.1.0)	1m 33s
stubtest	26s
test (latest, latest-release, latest-release, latest-release, latest-release)	2m 46s
test (minimum, 2025.07.1, 2025.2.0, 2025.2.0, 3.1.0)	2m 44s
	14m 49s

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