VecDeque<T> for double-ended queue operations

VecDeque<T> is a growable ring buffer supporting efficient push/pop from both ends. I use it for queues, breadth-first search, and sliding windows. Methods: .push_front(), .push_back(), .pop_front(), .pop_back() are all O(1). It's implemented as a circular buffer, so it reallocates less often than naive queue implementations. For FIFO queues, push to the back and pop from the front. For LIFO (stack), push and pop from the same end. VecDeque is more versatile than Vec for queue use cases but slightly slower for random access. It's the go-to for BFS and any algorithm that needs efficient dequeue operations.