feat: loop prop and public methods

[bradmartin]

• Adds loop prop so you can play the animation once or allow looping.
• Move play/pause methods to public for more control of playback.

This allows the following behavior:

 Image(uiImage: self.lottie.image)
                        .resizable()
                        .scaledToFit()
                        .onAppear {
                            self.lottie.loop = false
                            self.lottie.loadAnimationFromFile(filename: "green-success")
                            
                            DispatchQueue.main.asyncAfter(deadline: .now() + 5) {
                                self.lottie.play()
                                self.lottie.loop = true
                            }
                        }

So the animation plays once (since loop is false) then after a delay play() is called to start the animation again and loop = true to allow looping to occur.