obs: replace runtime.ReadMemStats with runtime/metrics

[lyang24]

This commit replaces Memstats collection with go runtime metrics. The latter approach do not require stw to collect memory stats.

A subtle change to be noted: statsProfiler still call runtime.ReadMemStats on spot when it determines memory stats should be saved. The previous behavior was to save with the Memstats that was refreshed periodically.

Fixes: https://github.com/cockroachdb/cockroach/issues/119461

Release note: None

Testing: Single node kv workload side by side comparison left=this commit and right=master memory gc pause time

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[cockroach-teamcity]

This change is 

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[lyang24]

After reading the doc i am fairly confident on all the new metrics from runtime/metrics.

This is a risky change at the end of the day, Hi @nvanbenschoten do you mind to take a second look when you have time

[lyang24]

bors r+

[craig[bot]]

Build succeeded:

• Bazel Essential CI (Cockroach)