[Feature] encodable/decodable for Signed transaction

[allnil]

Component

consensus, eips, genesis

Describe the feature you would like

alloy-consensus:
e.g: usual TxEip4844 implements Encodable/Decodable
But Signed doesn't
we should have the ability to encode/decode Signed transactions directly

Additional context

e.g at this moment we can't do this:

let mut encoded = Vec::new();
my_tx.encode_for_signing(&mut encoded);
let signature = local_wallet.sign_signable(&mut my_tx.clone()).unwrap();
let mut signed_tx = my_tx.clone().into_signed(signature);
let encoded = &alloy_rlp::encode(signed_tx); // trait `Encodable` is not implemented for `Signed<TxEip4844>` 

alloy/crates/consensus/src/signed.rs

Line 6 in f7333c4

pub struct Signed<T, Sig = Signature> {

we want the Encodable2718 trait, impl in TxEnvelope:

alloy/crates/consensus/src/transaction/envelope.rs

Line 216 in f7333c4

impl Encodable2718 for TxEnvelope {

[mattsse]

@prestwich I think what we want is

alloy/crates/eips/src/eip2718.rs

Line 124 in f7333c4

pub trait Encodable2718: Sized + Send + Sync + 'static {

for Signed<Tx>

we could either do this manually for all Signed<Tx*> types or make this

alloy/crates/consensus/src/transaction/envelope.rs

Lines 230 to 243 in f7333c4

	fn encode_2718(&self, out: &mut dyn alloy_rlp::BufMut) {
	match self {
	// Legacy transactions have no difference between network and 2718
	TxEnvelope::Legacy(tx) => tx.tx().encode_with_signature_fields(tx.signature(), out),
	TxEnvelope::Eip2930(tx) => {
	tx.tx().encode_with_signature(tx.signature(), out, false);
	}
	TxEnvelope::Eip1559(tx) => {
	tx.tx().encode_with_signature(tx.signature(), out, false);
	}
	TxEnvelope::Eip4844(tx) => {
	tx.tx().encode_with_signature(tx.signature(), out, false);
	}
	}

part of a trait, so we can do:

alloy/crates/consensus/src/signed.rs

Line 34 in f7333c4

impl<T: SignableTransaction<Sig>, Sig> Signed<T, Sig> {

[onbjerg]

You can do this by wrapping it in an envelope (TxEnvelope) which IIRC was intended, I vaguely remember the blanket impl for Signed<Tx> being removed by @Rjected in a recent PR

[prestwich]

It was removed, because it is often incorrect to use it, in a way that is not obvious to users. If people are asking for it, we should push them towards TxEnvelope more aggressively

[allnil]

Hmmm, okay! I'll take a look into the TxEnvelope
Thank you