refactor(lib): use non_exhaustive attribute #2499

Job	Run time
Verify hyper.h is up to date	30s
Check Style	12s
semver	15s
minimal-versions	31s
Test with Miri	1m 19s
Test C API (FFI)	22s
features	43s
Check MSRV	32s
Test stable on ubuntu-latest	2m 54s
udeps	38s
Test stable on windows-latest	2m 6s
Test stable on macOS-latest	2m 15s
Test beta on ubuntu-latest	1m 25s
Test beta on windows-latest	2m 47s
Test beta on macOS-latest	2m 38s
Test nightly on ubuntu-latest	1m 35s
Test nightly on windows-latest	2m 54s
Test nightly on macOS-latest	3m 46s
Build docs	23s
Check exposed types	15s
CI is green	1s
	28m 1s

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