Make use of Builder::serve_buffered_connection #435

Job	Run time
Check Style	10s
semver	17s
features	43s
Test with Miri	49s
Check MSRV (1.63)	2m 5s
Test stable on ubuntu-latest	42s
Test stable on windows-latest	1m 20s
Test stable on macos-latest	29s
Test beta on ubuntu-latest	37s
Test beta on windows-latest	1m 34s
Test beta on macos-latest	36s
Test nightly on ubuntu-latest	35s
Test nightly on windows-latest	1m 41s
Test nightly on macos-latest	36s
Build docs	12s
CI is green	1s
	12m 27s

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