Add support for `Bundle` inside `BundleItem`

[pinkshowercurtain]

What's the reason that mev-share-rs doesn't support using Bundle as a BundleItem?

I see that MEV-Share supports this.

pub enum BundleItem {
    /// The hash of either a transaction or bundle we are trying to backrun.
    Hash {
        /// Tx hash.
        hash: TxHash,
    },
    /// A new signed transaction.
    #[serde(rename_all = "camelCase")]
    Tx {
        /// Bytes of the signed transaction.
        tx: Bytes,
        /// If true, the transaction can revert without the bundle being considered invalid.
        can_revert: bool,
    },
}