Function compute_channel_id 

pub(super) fn compute_channel_id(
    payer: Address,
    payee: Address,
    token: Address,
    salt: B256,
    authorized_signer: Address,
    channel_address: Address,
    chain_id: u64,
) -> B256

Precompute the channel ID using the same formula as the contract.

channelId = keccak256(abi.encode(payer, payee, token, salt, authorizedSigner, channel, chainId))