Design a banking ledger for deposits/withdrawals

## Banking/OO Design: Account Ledger Design a minimal in-memory or persistent component for a bank account system that supports: - `deposit(account_id, amount)` - `withdraw(account_id, amount)` (reject if insufficient funds) - `transactionHistory(account_id)` (list transactions in chronological order) - `balance(account_id)` ### Requirements - Amounts are non-negative and use correct currency precision. - Concurrency: multiple operations may happen at the same time for the same account. - Avoid double-processing if a client retries a request (idempotency). Describe your data model and how you ensure correctness.