pkg/aflow: various improvements #19110

Job	Run time
gvisor	4m 58s
old	7m 30s
race	8m 47s
arch (presubmit_arch_openbsd)	3m 55s
arch (presubmit_arch_freebsd)	6m 34s
arch (presubmit_arch_netbsd)	3m 54s
arch (presubmit_arch_windows)	3m 46s
dashboard	2m 41s
arch (presubmit_arch_executor)	3m 17s
aux	4m 2s
arch (presubmit_arch_darwin)	3m 56s
race_dashboard	4m 2s
build	4m 53s
arch (presubmit_arch_linux)	10m 43s
	1h 12m 58s

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