refactor(lib): use non_exhaustive attribute #2439

Job	Run time
Verify hyper.h is up to date	19s
Check Style	11s
semver	18s
features	11s
Test with Miri	55s
Check MSRV	18s
Test stable on ubuntu-latest	1m 6s
Test C API (FFI)	25s
Test stable on windows-latest	2m 0s
minimal-versions	36s
Test stable on macOS-latest	2m 15s
udeps	26s
Test beta on ubuntu-latest	1m 12s
Test beta on windows-latest	2m 8s
Test beta on macOS-latest	1m 31s
Test nightly on ubuntu-latest	1m 16s
Test nightly on windows-latest	1m 56s
Test nightly on macOS-latest	1m 35s
Build docs	18s
Check exposed types	26s
CI is green	1s
	19m 23s

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