feat: add const `try_from_str` constructor to `DnsName` type. #845

Job	Run time
Clippy	5s
Smoke-test fuzzing targets	1m 7s
Build + test (stable, ubuntu-latest)	27s
Format	6s
Build + test (beta, ubuntu-latest)	38s
msrv (ubuntu-latest)	1m 40s
Build + test (nightly, ubuntu-latest)	34s
Check semver compatibility	6s
Check side-channels on base64 decoder	36s
msrv (macos-latest)	2m 2s
Build + test (macos-latest, stable)	17s
msrv (windows-latest)	2m 13s
Build + test (windows-latest, stable)	1m 5s
Build wasm32	17s
	11m 13s

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