Support PEM decoding for `EchConfigListBytes` #677

Job	Run time
Format	3s
Smoke-test fuzzing targets	1m 10s
Clippy	14s
Build + test (stable, ubuntu-latest)	53s
Build + test (beta, ubuntu-latest)	47s
msrv (ubuntu-latest)	47s
Check semver compatibility	8s
Check side-channels on base64 decoder	33s
Build + test (nightly, ubuntu-latest)	37s
msrv (macos-latest)	54s
Build + test (macos-latest, stable)	12s
msrv (windows-latest)	1m 3s
Build + test (windows-latest, stable)	1m 12s
Build wasm32	16s
	8m 49s

Provide feedback