feat(client): add Layer types for client::conn #853

Job	Run time
Check Style	10s
semver	18s
Check MSRV (1.63) on ubuntu-latest	27s
Check MSRV (1.63) on macos-latest	1m 58s
Check MSRV (1.63) on windows-latest	23s
Test with Miri	48s
features	37s
Test stable on ubuntu-latest	23s
Test beta on windows-latest	1s
Test stable on macos-latest	1s
Test stable on windows-latest	1s
Test beta on ubuntu-latest	1s
Test nightly on ubuntu-latest	1s
Test beta on macos-latest	1s
Test nightly on windows-latest	1s
Test nightly on macos-latest	1s
Build docs	0s
CI is green	0s
	5m 12s

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