Save ZJIT stats_string to JSON output for stats collection (#475) #1705

Job	Run time
test (head)	42s
test (truffleruby)	1m 40s
benchmark-ractor (head)	6m 48s
benchmark-graph	41s
benchmark-default (head)	13m 53s
benchmark-run-once	1m 39s
benchmark-ractor-only (head)	39s
benchmark-default (ruby)	13m 38s
test (ruby)	1m 5s
benchmark-default (truffleruby, --excludes=knucleotide,lobsters,ruby-lsp,shipit)	13m 5s
all-tests	3s
	53m 53s

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