Function build_open_and_close 

pub(super) fn build_open_and_close(
    channel_address: Address,
    payer: Address,
    token: Address,
    salt: B256,
    channel_id: B256,
) -> TempoTransactionRequest

Build a TempoTransactionRequest with two calls: channel open + close.

The signer is both payer and payee, so close succeeds immediately.