Add comments for BidiQueue, BidiQueueEnd, and Queue

namespace bluetooth {

namespace common {

//

// Interface for one context to send and receive data over

// a pair of queues (|BidiQueue|).

//

template <typename TENQUEUE, typename TDEQUEUE>

class BidiQueueEnd : public ::bluetooth::os::IQueueEnqueue<TENQUEUE>,

                     public ::bluetooth::os::IQueueDequeue<TDEQUEUE> {

  ::bluetooth::os::IQueueDequeue<TDEQUEUE>* rx_;

};

//

// Interface managing a pair of queues shared between two contexts

// (typically layers of the stack).

//

// The up queue can be used for data to indicate up to bluetooth host and

// the down queue can be used for data to sent to bluetooth controller.

// Each context uses its |BidiQueueEnd| to manage their data operations:

//

// The up end:

// - Receives data indicated from the down end.

// - Sends data to the down end.

//

// The down end:

// - Receives data sent from the up end.

// - Indicates data to the up end.

//

template <typename TUP, typename TDOWN>

class BidiQueue {

public:

  virtual std::unique_ptr<T> TryDequeue() = 0;

};

//

// An interface facilitating flow-controlled and non-blocking queue operations.

//

// This Queue uses separate semaphores and callbacks for enqueue end (producer)

// and dequeue end (consumer) to manage data flow efficiently:

//

// Enqueue end (producer):

// - Registers an EnqueueCallback when producer has data to send.

// - Unregisters the EnqueueCallback when no data is available.

//

// Dequeue end (consumer):

// - Registers a DequeueCallback when consumer is ready to process data.

// - Unregisters the DequeueCallback when no longer ready.

//

template <typename T>

class Queue : public IQueueEnqueue<T>, public IQueueDequeue<T> {

public: