Move OkValidator into txpool behind test-utils feature gate

[mattsse]

Describe the feature

This is quite useful:

reth/examples/network-txpool/src/main.rs

Lines 78 to 103 in b36201b

	#[derive(Debug, Default)]
	#[non_exhaustive]
	struct OkValidator;
	impl TransactionValidator for OkValidator {
	type Transaction = EthPooledTransaction;
	async fn validate_transaction(
	&self,
	_origin: TransactionOrigin,
	transaction: Self::Transaction,
	) -> TransactionValidationOutcome<Self::Transaction> {
	// Always return valid
	let authorities = transaction.authorization_list().map(|auths| {
	auths.iter().flat_map(|auth| auth.recover_authority()).collect::<Vec<_>>()
	});
	TransactionValidationOutcome::Valid {
	balance: *transaction.cost(),
	state_nonce: transaction.nonce(),
	bytecode_hash: None,
	transaction: ValidTransaction::Valid(transaction),
	propagate: false,
	authorities,
	}
	}
	}

we can make this available from the pool itself, if we feature gate this behind test-utils and relax the type with a new PhantomType generic

Additional context

No response

[Rimeeeeee]

May I look into this :)