NewFifoQueue is the Constructor for FifoQueue.

WithLengthMetricObserver attaches a length observer which calls the given observe function.

WithLengthObserver is a constructor option for NewFifoQueue.

CapacityUnlimited specifies the largest possible capacity for a FifoQueue.

FifoQueue implements a FIFO queue with max capacity and length observer.

ConstructorOptions are optional arguments for the `NewFifoQueue` constructor to specify properties of the FifoQueue.

QueueLengthObserver is a optional callback that can be provided to the `NewFifoQueue` constructor (via `WithLengthObserver` option).