tests

Simplify vendoring and declare dependencies optionally #4865

Job	Run time
test_cygwin (39, windows-latest)	16m 48s
collateral (diffcov)	5m 15s
test (3.8, ubuntu-latest)	3m 48s
collateral (docs)	1m 48s
test (3.8, windows-latest)	11m 21s
test (3.12, ubuntu-latest)	5m 49s
test (3.12, macos-latest)	4m 9s
test (3.12, windows-latest)	9m 45s
test (3.9, ubuntu-latest)	4m 4s
test (3.10, ubuntu-latest)	3m 45s
test (3.11, ubuntu-latest)	3m 42s
test (pypy3.10, ubuntu-latest, stdlib)	15m 53s
test (ubuntu-latest, 3.10, stdlib)	3m 47s
test (3.8, macos-13)	6m 29s
integration-test	0s
check	2s
release	0s
	1h 36m 25s

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