ZJIT: Use a slice for ISeq `opt_table` for quick one-off access #12819

Job	Run time
make (check, cppflags=-DVM_CHECK_MODE)	8m 29s
make (check, i686)	11m 15s
make (check, --disable-yjit)	7m 2s
ruby-bench (--warmup=1 --bench=1 --excludes=shipit)	13m 57s
make (check, --enable-shared --enable-load-relative)	7m 51s
make (test-bundler-parallel, 50)	22m 20s
make (check, ubuntu-24.04, capi)	9m 55s
make (test-bundled-gems)	13m 24s
make-ibm	-1s
Ubuntu result	3s
	1h 34m 15s

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