Support PEM decoding for `EchConfigListBytes` #688

Job	Run time
Format	4s
Clippy	13s
Build + test (stable, ubuntu-latest)	36s
Build + test (beta, ubuntu-latest)	30s
Smoke-test fuzzing targets	1m 19s
Build + test (nightly, ubuntu-latest)	40s
msrv (ubuntu-latest)	45s
msrv (macos-latest)	49s
Build + test (macos-latest, stable)	15s
Check semver compatibility	8s
Build + test (windows-latest, stable)	40s
msrv (windows-latest)	1m 7s
Check side-channels on base64 decoder	32s
Build wasm32	28s
	8m 6s

Provide feedback