Derive rlp en-/decoding for `Sealed<T>` #2043

Job	Run time
test ubuntu-latest stable --no-default-features	1m 18s
check no_std	54s
test ubuntu-latest stable	1m 28s
clippy	38s
test ubuntu-latest nightly --no-default-features	1m 18s
test ubuntu-latest nightly	1m 21s
features stable	2m 44s
test ubuntu-latest 1.79 --no-default-features	38s
miri --no-default-features	5m 0s
features stable --all-targets	3m 38s
features nightly	2m 26s
miri	5m 7s
test ubuntu-latest 1.79	41s
features nightly --all-targets	3m 33s
miri --all-features	5m 34s
wasm	40s
docs	55s
test windows-latest stable --no-default-features	2m 56s
test windows-latest stable	2m 44s
fmt	12s
test windows-latest nightly --no-default-features	2m 47s
test windows-latest nightly	2m 40s
test windows-latest 1.79 --no-default-features	1m 40s
test windows-latest 1.79	1m 27s
test ubuntu-latest 1.79 --features json	38s
test windows-latest 1.79 --features json	1m 33s
test ubuntu-latest nightly --all-features	1m 25s
test windows-latest nightly --all-features	3m 4s
	58m 59s

Provide feedback