Make use of Builder::serve_buffered_connection #441

Job	Run time
Check Style	4s
semver	17s
Check MSRV (1.63)	2m 6s
Test with Miri	51s
features	46s
Test stable on ubuntu-latest	38s
Test stable on windows-latest	2m 32s
Test stable on macos-latest	28s
Test beta on ubuntu-latest	36s
Test beta on windows-latest	1m 29s
Test beta on macos-latest	54s
Test nightly on ubuntu-latest	36s
Test nightly on windows-latest	1m 11s
Test nightly on macos-latest	35s
Build docs	14s
CI is green	1s
	13m 18s

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