fix: Log `rttvar` in qlog #3356

Job	Run time
Build & test (ubuntu-latest, 1.76.0, debug)	11m 3s
Build & test (ubuntu-latest, stable, debug)	10m 58s
Build & test (ubuntu-latest, nightly, debug)	11m 16s
Build & test (macos-14, 1.76.0, debug)	9m 56s
Build & test (macos-14, stable, debug)	9m 41s
Build & test (macos-14, nightly, debug)	11m 1s
Build & test (windows-latest, 1.76.0, debug)	19m 13s
Build & test (windows-latest, stable, debug)	24m 38s
Build & test (windows-latest, nightly, debug)	21m 27s
Build & test (ubuntu-latest, stable, release)	16m 11s
Benchmark / Benchmark	15m 29s
	2h 40m 53s

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