Move the methods to prepare the benchmark outputs to the BenchmarkRunner class #1500

Job	Run time
benchmark-default (truffleruby)	27s
benchmark-default (ruby)	11m 24s
benchmark-default (head)	11m 1s
test (head)	44s
test (ruby)	1m 8s
test (truffleruby)	1m 4s
benchmark-ractor (ruby)	12m 52s
benchmark-ractor (head)	12m 18s
benchmark-ractor (truffleruby)	18s
benchmark-ractor-only (head)	47s
benchmark-ractor-only (ruby)	55s
benchmark-ractor-only (truffleruby)	14s
benchmark-run-once	1m 39s
benchmark-graph	51s
all-tests	2s
	55m 44s

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