feat: add stateless validator

[ArniStarkware]

This change is 

[ArniStarkware]

crates/gateway/src/transaction_validator.rs line 15 at r1 (raw file):

// TODO(Arni, 1/5/2024): Remove the this value if we use a type which supports version 3 and above
// only.
// It is an assumption of this repository that the minimal supported transaction version is 3.

Delete.

Code quote:

// TODO(Arni, 1/5/2024): Remove the this value if we use a type which supports version 3 and above
// only.
// It is an assumption of this repository that the minimal supported transaction version is 3.

[ArniStarkware]

Reviewable status: 0 of 6 files reviewed, 2 unresolved discussions (waiting on @dafnamatsry)

---

crates/gateway/src/errors.rs line 33 at r1 (raw file):

    BlockedTransactionVersion(TransactionVersion, String),
    #[error("This transaction type is not supported by the mempool")]
    TransactionTypeNotSupported,

Remove.

Code quote:

    #[error("Transactions of version {0:?} are not valid. {1}")]
    InvalidTransactionVersion(TransactionVersion, String),
    #[error("Blocked transaction version {0:?}. {1}")]
    BlockedTransactionVersion(TransactionVersion, String),
    #[error("This transaction type is not supported by the mempool")]
    TransactionTypeNotSupported,

[ArniStarkware]

Will be replaced with a tower.