docs: developer docs for the universal unit tests #8332

Job	Run time
Test Python (1, 3.8)	24m 51s
Test Python (1, 3.11)	24m 7s
Test Python (2, 3.8)	24m 5s
Test Python (2, 3.11)	22m 39s
Test Python (3, 3.8)	23m 20s
Test Python (3, 3.11)	23m 11s
Test Python (4, 3.8)	22m 52s
Test Python (4, 3.11)	24m 15s
Test Python (5, 3.8)	23m 23s
Test Python (5, 3.11)	22m 44s
Test Python (6, 3.8)	24m 30s
Test Python (6, 3.11)	22m 59s
Combine and update integration test durations (3.8)	5s
Combine and update integration test durations (3.11)	18s
Pass testing Python	1s
	4h 43m 20s

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