[nextest-runner] move a few pieces of code into separate functions #2442

Job	Run time
Build documentation (ubuntu-latest)	1m 36s
Build and test (ubuntu-latest, 1.70)	6m 23s
Lint	40s
Test archives with a target runner	2m 20s
Build and test (ubuntu-latest, stable)	4m 54s
Build and test (macos-latest, 1.70)	8m 3s
Build and test (macos-latest, stable)	6m 11s
Build and test (windows-latest, 1.70)	9m 10s
Build and test (windows-latest, stable)	11m 33s
	50m 50s

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