quinn-proto: Fix RTT measurements with max_ack_delay timer resolution #7074

Job	Run time
lint	1m 22s
test on freebsd	4m 37s
test wasm32-unknown-unknown	1m 27s
features (ubuntu-latest)	23m 42s
test-aws-lc-rs	3m 15s
audit	24s
test (windows-latest, stable)	2m 23s
features (windows-latest)	20m 14s
test on illumos	6m 28s
test (macos-latest, stable)	2m 21s
test on solaris	7m 0s
test-android (i686-linux-android, x86, 26)	2m 32s
features (macos-latest)	26m 1s
test-android (x86_64-linux-android, x86_64, 26)	2m 39s
msrv	1m 27s
test (ubuntu-latest, stable)	1m 51s
test-android (x86_64-linux-android, x86_64, 25)	2m 27s
test-android (i686-linux-android, x86, 25)	2m 19s
test (ubuntu-latest, beta)	1m 46s
	1h 54m 15s

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