message: Added NSCopying protocol to interface
diff: NS_ASSUME_NONNULL_BEGIN
  /** Holds a confidence mask belonging to a single class and its meta data. */
  -@interface TFLConfidenceMask : NSObject
  +@interface TFLConfidenceMask : NSObject <NSCopying>
  /**
  * Confidence masks of size `width` x `height` for any one class.
  @@ -46,7 +46,7 @@ NS_ASSUME_NONNULL_BEGIN
  @end
  /** Holds category mask and its metadata. */
  -@interface TFLCategoryMask : NSObject
  +@interface TFLCategoryMask : NSObject <NSCopying>
  /**
  * Flattened 2D-array of size `width` x `height`, in row major order.
  