Two-phase locking simulator

Simulate strict two-phase locking (S2PL) with a deterministic grant policy to detect blocking. ops is a list of [txn, action, key] in order. action is 'lock' (acquire an exclusive lock on key) or 'commit' (release ALL locks the txn holds). A 'lock' request is GRANTED immediately if the key is unlocked; otherwise the requesting txn BLOCKS and the op is recorded as a block. Once a txn is blocked on a key, it cannot issue further ops until unblocked, but to keep this deterministic, assume blocked requests are simply recorded and SKIPPED (the txn's later ops still process). When a 'commit' releases a key that has blocked waiters, the LONGEST-waiting blocked txn for that key (earliest block, by op index) is retried and, if now grantable, granted (recorded as a grant at the commit's position). Return a list of [op_index, txn, 'grant' | 'block'] for every lock request and every retry-grant, in chronological order of when they resolve.