potential cpu usage improvement for metrics

[lmatz]

From discussion with @Li0k and @Little-Wallace:

when running TPC-H q4 and generating CPU flamegraph: https://buildkite.com/risingwave-test/tpch-benchmark/builds/1014#018e0e57-a87f-4d2c-948a-7e2ecae8b3be

It was found that

Adding all 4 occurrences together, it is about 5% CPU time for metrics. q4 is a relatively simple query with only one join operator. The query can be found here: #14811

[lmatz]

It turns out there is 10% improvement for TPC-H q4: http://metabase.risingwave-cloud.xyz/question/13146-tpch-q4-bs-medium-1cn-affinity-avg-source-output-rows-per-second-rows-s-history-thtb-367?start_date=2024-01-25

execution id: 22223

[lmatz]

done by #15488