chore(sdk): SignedTransaction abstraction

[emhane]

Closes #11253

Checks out the abstraction of TransactionSigned from #11348 and #11352

[mattsse]

hmm, I really don't want to define new rlp functions on transaction trait now that we almost entirely on De/Encodable2718

could we start with something basic like Transaction: Encodable2718 + Decodeable2718?

[mattsse]

we def need this trait, but this should be moved to the traits crate.

and we should try without introducing new rlp functions, we should manage without and instead require that this type is also De/Encodeable2718

[emhane]

we def need this trait, but this should be moved to the traits crate.

and we should try without introducing new rlp functions, we should manage without and instead require that this type is also De/Encodeable2718

pr doesn't introduce any new methods at all. method deprecated in #11218 is removed in commit b820aa8.

[emhane]

re-request review @mattsse

[mattsse]

I feel like this already does too much.

I'd like to start very simple with a very simplistic trait

[mattsse]

cool, lgtm!