De-flake conformance CI: solo re-verification, spawn-storm reduction, result artifacts #3300

Job	Run time
checks / readme-snippets	11s
checks / test (3.13, lowest-direct, windows-latest)	2m 18s
checks / docs	46s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 18s
checks / test (3.13, locked, ubuntu-latest)	1m 16s
checks / pre-commit	54s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 8s
checks / test (3.14, locked, windows-latest)	2m 40s
checks / test (3.14, locked, ubuntu-latest)	2m 19s
checks / test (3.10, lowest-direct, windows-latest)	1m 56s
checks / test (3.10, locked, ubuntu-latest)	1m 30s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 28s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 27s
checks / test (3.12, locked, windows-latest)	2m 4s
checks / test (3.10, locked, windows-latest)	2m 4s
checks / test (3.11, locked, windows-latest)	1m 52s
checks / test (3.11, locked, ubuntu-latest)	1m 25s
checks / test (3.11, lowest-direct, windows-latest)	1m 49s
checks / test (3.13, locked, windows-latest)	1m 45s
checks / test (3.14, lowest-direct, windows-latest)	1m 49s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 23s
checks / test (3.12, lowest-direct, windows-latest)	2m 5s
checks / test (3.12, locked, ubuntu-latest)	1m 37s
all-green	2s
	37m 6s

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