Separate harness implementation from the harness framework #1531

Job	Run time
benchmark-default (head)	10m 41s
benchmark-default (truffleruby)	14m 13s
test (ruby)	1m 0s
benchmark-default (ruby)	11m 3s
test (head)	58s
benchmark-ractor (ruby)	12m 46s
benchmark-ractor (head)	12m 20s
benchmark-ractor-only (ruby)	55s
benchmark-ractor-only (head)	45s
test (truffleruby)	55s
benchmark-graph	51s
benchmark-run-once	1m 33s
all-tests	3s
	1h 8m 3s

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