feat(tests): overhaul staging test infrastructure and update fixtures #1462

Job	Run time
Collect changes / collect-changes	13s
Python tests / lint-and-format-check	20s
Python tests / docs-scripts-tests	28s
Python tests / unit-tests (py310)	3m 20s
Python tests / unit-tests (py311)	3m 25s
Python tests / unit-tests (py312)	2m 34s
Python tests / unit-tests (py314)	2m 25s
Python tests / unit-tests (py313)	2m 35s
Python tests / types-check	24s
status-check	4s
	15m 48s

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