Separate harness implementation from the harness framework #1530

Job	Run time
test (truffleruby)	1m 3s
test (ruby)	1m 8s
benchmark-default (ruby)	11m 1s
test (head)	1m 6s
benchmark-ractor-only (head)	49s
benchmark-default (truffleruby)	14m 40s
benchmark-ractor-only (ruby)	54s
benchmark-ractor (head)	12m 16s
benchmark-graph	55s
benchmark-default (head)	10m 53s
benchmark-run-once	1m 33s
benchmark-ractor (ruby)	12m 46s
all-tests	2s
	1h 9m 6s

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