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Add multi-Ractor memory benchmarks #2099

Job	Run time
test (ruby)	51s
benchmark-ractor-only (head)	53s
benchmark-graph	53s
test (head)	40s
benchmark-ractor (head)	6m 57s
test (truffleruby)	1m 26s
benchmark-default (head)	8m 30s
benchmark-default (ruby)	12m 24s
benchmark-default (truffleruby, --excludes=knucleotide,lobsters,ruby-lsp,shipit)	10m 0s
benchmark-run-once	1m 28s
all-tests	2s
	44m 4s