Make use of Builder::serve_buffered_connection #434

Job	Run time
Check Style	7s
semver	21s
features	47s
Test stable on ubuntu-latest	31s
Test with Miri	49s
Test stable on windows-latest	2m 37s
Check MSRV (1.63)	1m 59s
Test stable on macos-latest	30s
Test beta on ubuntu-latest	37s
Test beta on windows-latest	1m 23s
Test beta on macos-latest	42s
Test nightly on ubuntu-latest	35s
Test nightly on windows-latest	1m 45s
Test nightly on macos-latest	36s
Build docs	13s
CI is green	1s
	13m 33s

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