refactor(lib): use non_exhaustive attribute #2449

Job	Run time
Verify hyper.h is up to date	28s
Check Style	7s
semver	15s
Check MSRV	26s
Test C API (FFI)	37s
minimal-versions	25s
features	30s
Test with Miri	47s
Test stable on ubuntu-latest	1m 2s
udeps	29s
Test stable on windows-latest	1m 56s
Test stable on macOS-latest	1m 20s
Test beta on ubuntu-latest	1m 7s
Test beta on windows-latest	1m 56s
Test beta on macOS-latest	1m 56s
Test nightly on ubuntu-latest	1m 12s
Test nightly on windows-latest	2m 15s
Test nightly on macOS-latest	1m 56s
Build docs	14s
Check exposed types	19s
CI is green	1s
	19m 18s

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