Ensure a class has only one instance, and provide a global point of access to it — every call to getInstance() must return the exact same object, so state persists across "modules" that each grab their own reference.
Implement `Counter.getInstance()` so it lazily creates the instance once and reuses it forever after, plus increment()/getValue() on that instance.
solve(ops) runs a sequence of 'increment' | 'getValue' operations against Counter.getInstance(), collecting the results of every 'getValue' call.
solve(['increment', 'increment', 'getValue']) → [2] — both increments landed on the same instance.
Sample tests