Optimize OpTxpool 2718 bytes encoding

[mattsse]

Describe the feature

we currently do during validation:

reth/crates/optimism/txpool/src/validator.rs

Lines 271 to 273 in 4f4986c

	let mut encoded = Vec::with_capacity(valid_tx.transaction().encoded_length());
	let tx = valid_tx.transaction().clone_into_consensus();
	tx.encode_2718(&mut encoded);

because we need this to check for sufficient funds to cover the L1 DA fee

but we currently throw this away after validation.
instead we could obtain this from the tx itself, which would then just call:

reth/crates/optimism/txpool/src/transaction.rs

Lines 76 to 79 in 4f4986c

	/// Returns lazily computed EIP-2718 encoded bytes of the transaction.
	pub fn encoded_2718(&self) -> &Bytes {
	self.encoded_2718.get_or_init(|| self.inner.transaction().encoded_2718().into())
	}

then we'd already have the bytes stored for building.

to do this we need a way to call this generically, because rn this is restricted to:

reth/crates/optimism/txpool/src/validator.rs

Line 95 in 4f4986c

Tx: EthPoolTransaction + MaybeInteropTransaction,

so need a trait function that returns

fn encoded_2718(&self) -> Cow<Bytes>

we can add this to the existing OpPooledTx

reth/crates/optimism/txpool/src/transaction.rs

Line 282 in 4f4986c

pub trait OpPooledTx:

and update the restriction in the implementation to OpPooledTx

Additional context

No response

[fantasyup]

Can I take this too?