feat(starknet_api): derive serialize for executable transaction

[MohammadNassar1]

This change is 

[giladchase]

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @ayeletstarkware and @elintul)

[giladchase]

BTW i think you can rebase this onto main and insert directly.
Yr Prs using it will temporarily fail CI, not too bad since this can be merged quickly

Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @ayeletstarkware and @elintul)

[MohammadNassar1]

Done

Reviewable status: all files reviewed (commit messages unreviewed), all discussions resolved (waiting on @ayeletstarkware and @elintul)

[giladchase]

Reviewed all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @ayeletstarkware and @elintul)

[ArniStarkware]

crates/starknet_api/src/executable_transaction.rs line 64 at r2 (raw file):

    pub tx_hash: TransactionHash,
    pub class_info: ClassInfo,
}

If we want to use Blockifier's ClassInfo, we have a problem: it cannot derive serialize.

Code quote:

// TODO(Mohammad): Add constructor for all the transaction's structs.
#[derive(Clone, Debug, Deserialize, Eq, PartialEq, Serialize)]
pub struct DeclareTransaction {
    pub tx: crate::transaction::DeclareTransaction,
    pub tx_hash: TransactionHash,
    pub class_info: ClassInfo,
}