Deadlock-free transfers with tryLock

Implement static boolean transfer(Account from, Account to, int amount) that can NEVER deadlock, using the tryLock-backoff pattern: 1. Acquire both account locks with tryLock() (use a small retry loop with backoff or a ordered attempt). 2. On success: check from.balance() >= amount, then move funds, release both locks, return true. 3. If either lock cannot be acquired: release whatever you hold and return false. 4. record Account(int id, int balance) won't do — accounts must expose ReentrantLock lock() and be mutable; build a small static Account class inside Solution (id, balance, lock). 5. static boolean unsafeTransfer(...) doing the same with plain synchronized(from) nested synchronized(to) — intentionally deadlock-prone in *structure* (tests only call it with distinct orderings to keep the suite deterministic; the lesson explains the hazard).

Difficulty: advanced