Implement an in-memory banking system that processes API calls in nondecreasing `timestamp` order. Support the following operations: - `create_account(timestamp, account_id) -> bool` - Create a new account with balance `0`. - Return `false` if the account already exists; otherwise return `true`. - `deposit(timestamp, account_id, amount) -> int | None` - Add `amount` to the account balance. - Return the updated balance. - Return `None` if the account does not exist. - `transfer(timestamp, source, target, amount) -> int | None` - Move `amount` from `source` to `target`. - Return the updated balance of `source`. - Return `None` if either account does not exist, `source == target`, or `source` has insufficient funds. - `top_spenders(timestamp, n) -> list[str]` - Return up to `n` accounts with the largest total outgoing amount. - Format each result as `"account_id(total_outgoing)"`. - Sort by total outgoing amount in descending order; break ties by `account_id` in ascending lexicographic order. - Outgoing amount includes money successfully sent out of an account. - `schedule_payment(timestamp, account_id, amount, delay) -> str | None` - Schedule a withdrawal of `amount` from `account_id` at time `timestamp + delay`. - Return a globally unique payment ID such as `"payment1"`, `"payment2"`, and so on. - Return `None` if the account does not exist. - `cancel_payment(timestamp, account_id, payment_id) -> bool` - Cancel a pending scheduled payment. - Return `true` only if the payment exists, belongs to `account_id`, and has not already executed or been canceled. - `merge_accounts(timestamp, account_id_1, account_id_2) -> bool` - Merge `account_id_2` into `account_id_1`. - The surviving account keeps `account_id_1`. - Its balance becomes the sum of both balances. - Its outgoing total becomes the sum of both outgoing totals. - Any pending scheduled payments owned by `account_id_2` are transferred to `account_id_1`. - `account_id_2` is then deleted. - Return `false` if either account does not exist or the two IDs are the same. - `get_balance(timestamp, account_id, time_at) -> int | None` - Return the balance of `account_id` at historical time `time_at`. - Return `None` if the account does not exist at query time or if `time_at` is earlier than the account's creation time. Additional assumptions to make the problem self-contained: - All amounts are nonnegative integers. - Whenever an operation is called at time `t`, all scheduled payments due at or before `t` must be processed before the operation itself. - If multiple scheduled payments are due at the same time, process them in payment creation order. - A scheduled payment executes only if the owning account has sufficient funds at execution time; otherwise it is skipped.