De-flake conformance CI: solo re-verification, spawn-storm reduction, result artifacts #3298

Job	Run time
checks / docs	46s
checks / readme-snippets	15s
checks / pre-commit	46s
checks / test (3.11, lowest-direct, windows-latest)	1m 58s
checks / test (3.13, lowest-direct, windows-latest)	2m 5s
checks / test (3.11, locked, ubuntu-latest)	1m 21s
checks / test (3.13, locked, ubuntu-latest)	1m 13s
checks / test (3.12, locked, windows-latest)	2m 23s
checks / test (3.11, locked, windows-latest)	1m 56s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 22s
checks / test (3.12, lowest-direct, windows-latest)	1m 59s
checks / test (3.14, lowest-direct, windows-latest)	2m 1s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 19s
checks / test (3.10, lowest-direct, windows-latest)	1m 54s
checks / test (3.14, locked, ubuntu-latest)	2m 0s
checks / test (3.10, locked, ubuntu-latest)	1m 24s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 24s
checks / test (3.10, locked, windows-latest)	1m 36s
checks / test (3.13, locked, windows-latest)	1m 59s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 19s
checks / test (3.14, locked, windows-latest)	2m 37s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 22s
checks / test (3.12, locked, ubuntu-latest)	1m 32s
all-green	6s
	36m 37s

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