Add --zjit-mem flag to show ZJIT memory stats in summary table

[k0kubun]

Show code_region_bytes and zjit_alloc_bytes per executable in the summary table when --zjit-mem is passed.

Example:

$ ./run_benchmarks.rb lobsters --chruby 'before --zjit;after --zjit' --zjit-mem --no-sudo --warmup=1 --bench=1
Running benchmark "lobsters" (1/1)
+ setarch x86_64 -R taskset -c 10 /opt/rubies/before/bin/ruby --zjit -I harness /home/k0kubun/src/github.com/ruby/ruby-bench/benchmarks/lobsters/benchmark.rb
ruby 4.1.0dev (2026-03-24T17:47:36Z master-iseq 756c801f50) +ZJIT +PRISM [x86_64-linux]
Command: bundle check 2> /dev/null || bundle install
The Gemfile's dependencies are satisfied
itr:   time
 #1: 2015ms
 #2:  913ms
ZJIT stats:
code_region_bytes:     10,579,968
zjit_alloc_bytes:      13,726,764
compile_time            1891.17ms
profile_time              17.73ms
gc_time                   15.27ms
invalidation_time         11.85ms
RSS: 333.0MiB
MAXRSS: 334.2MiB
Running benchmark "lobsters" (1/1)
+ setarch x86_64 -R taskset -c 10 /opt/rubies/after/bin/ruby --zjit -I harness /home/k0kubun/src/github.com/ruby/ruby-bench/benchmarks/lobsters/benchmark.rb
ruby 4.1.0dev (2026-03-24T21:47:14Z master 30dcc2a082) +ZJIT +PRISM [x86_64-linux]
Command: bundle check 2> /dev/null || bundle install
The Gemfile's dependencies are satisfied
itr:   time
 #1: 2014ms
 #2:  872ms
ZJIT stats:
code_region_bytes:      9,736,192
zjit_alloc_bytes:      13,746,992
compile_time            1891.66ms
profile_time              17.62ms
gc_time                   15.87ms
invalidation_time         12.28ms
RSS: 331.3MiB
MAXRSS: 332.6MiB
Total time spent benchmarking: 14s

before: ruby 4.1.0dev (2026-03-24T17:47:36Z master-iseq 756c801f50) +ZJIT +PRISM [x86_64-linux]
after: ruby 4.1.0dev (2026-03-24T21:47:14Z master 30dcc2a082) +ZJIT +PRISM [x86_64-linux]

--------  ------------  ----------  ----------  ------------  ---------  ----------  -------------  ------------
bench      before (ms)    code (B)   alloc (B)    after (ms)   code (B)   alloc (B)  after 1st itr  before/after
lobsters  913.8 ± 0.0%  10,579,968  13,726,764  872.1 ± 0.0%  9,736,192  13,746,992          1.000         1.048
--------  ------------  ----------  ----------  ------------  ---------  ----------  -------------  ------------