Print Zero, Even, Odd in Order

**Concurrency design problem (paper-only).** This problem exercises threading / synchronisation primitives that the gitGood code-execution sandbox does not expose. The auto-grader instead validates a single-threaded *simulation* of the protocol so you can still verify your scheduler logic; in a real interview you would write the multi-threaded version. You have a class `ZeroEvenOdd` shared by three threads: - Thread A repeatedly calls `zero()`, which prints `0`. - Thread B repeatedly calls `even()`, which prints an even number. - Thread C repeatedly calls `odd()`, which prints an odd number. For a given integer `n`, the three threads collectively print the sequence `0102030405...` up through `n`, i.e. for `n = 5` the output is `"0102030405"`. The threads coordinate using two semaphores (one gating `even`, one gating `odd`). Thread A toggles which side it releases after each zero. **For the auto-grader:** implement `zeroEvenOdd(n)` that returns the string the three threads would collectively produce for input `n`. Your single-threaded simulation must follow the protocol described in the explanation (don't just return `"01020304..."` by string concatenation - work through the state machine).