Adds --blockhash arg to Close

[brooksprumo]

I'd like the --blockhash arg on the Close instruction. This is done by calling .offline_args().

output from `spl-token close --help`

spl-token-close 
Close a token account

USAGE:
    spl-token close [OPTIONS] [--] [TOKEN_MINT_ADDRESS]

ARGS:
    <TOKEN_MINT_ADDRESS>    Token of the associated account to close. To close a specific
                            account, use the `--address` parameter instead

OPTIONS:
        --address <TOKEN_ACCOUNT_ADDRESS>
            Specify the token account to close [default: owner's associated token account]

        --blockhash <BLOCKHASH>
            Use the supplied blockhash

    -C, --config <PATH>
            Configuration file to use

        --close-authority <KEYPAIR>
            Specify the token's close authority if it has one, otherwise specify the token's owner
            keypair. This may be a keypair file or the ASK keyword. Defaults to the client keypair.

        --dump-transaction-message
            Display the base64 encoded binary transaction message in sign-only mode

        --fee-payer <KEYPAIR>
            Specify the fee-payer account. This may be a keypair file, the ASK keyword
            or the pubkey of an offline signer, provided an appropriate --signer argument
            is also passed. Defaults to the client keypair.

    -h, --help
            Print help information

        --multisig-signer [<MULTISIG_SIGNER>...]
            Member signer of a multisig account

        --nonce <PUBKEY>
            Provide the nonce account to use when creating a nonced
            transaction. Nonced transactions are useful when a transaction
            requires a lengthy signing process. Learn more about nonced
            transactions at https://docs.solanalabs.com/cli/examples/durable-nonce

        --nonce-authority <KEYPAIR>
            Provide the nonce authority keypair to use when signing a nonced transaction

        --output <FORMAT>
            Return information in specified output format [possible values: json, json-compact]

        --owner <OWNER_ADDRESS>
            Address of the primary authority controlling a mint or account. Defaults to the client
            keypair address.

    -p, --program-id <ADDRESS>
            SPL Token program id

        --program-2022
            Use token extension program token 2022 with program id:
            TokenzQdBNbLqP5VEhdkAS6EPFLC1PHnBqCXEpPxuEb

        --recipient <REFUND_ACCOUNT_ADDRESS>
            The address of the account to receive remaining SOL [default: --owner]

        --sign-only
            Sign the transaction offline

        --signer <PUBKEY=SIGNATURE>
            Provide a public-key/signature pair for the transaction

    -u, --url <URL_OR_MONIKER>
            URL for Solana's JSON RPC or moniker (or their first letter): [mainnet-beta, testnet,
            devnet, localhost] Default from the configuration file.

    -v, --verbose
            Show additional information

        --with-compute-unit-limit <COMPUTE-UNIT-LIMIT>
            Set compute unit limit for transaction, in compute units.

        --with-compute-unit-price <COMPUTE-UNIT-PRICE>
            Set compute unit price for transaction, in increments of 0.000001 lamports per compute
            unit.

[joncinque]

The change looks good to me! The close implementation already takes into account the sign_only field, so this should be the only change needed.

Once you've had a chance to try this locally just to double-check, we can merge it. Thanks for your contribution!