Print ZJIT time stats at the end

[k0kubun]

This PR lets benchmark harnesses print ZJIT time stats after benchmarks.

While it's possible to print all stats with --zjit-stats, we want to see some of the stats without --zjit-stats because it compiles more code and thus significantly impacts some of the stats. To check the real compile-time overhead, for example, we want to see :compile_time_ns without enabling --zjit-stats. So this harness prints it automatically, similarly to those YJIT stats.

I'll also add :code_region_size here once it's added to ZJIT stats.