feat: expose playback speed control to Flutter on iOS

[Nisarg-18]

Wire up the existing native iOS setSpeed implementation to Flutter through the full method channel pipeline:

• Add "setSpeed" case to iOS method channel handler in FLTBetterPlayerPlugin
• Simplify iOS setSpeed() to remove overly restrictive capability checks
• Add setSpeed() to VideoPlayerPlatform interface
• Add setSpeed() to MethodChannelVideoPlayer
• Add setSpeed() to VideoPlayerController
• Add setSpeed() to BetterPlayerController with error handling

The Android side already had this wired up via BetterPlayerPlugin.java.

Speed range is 0.0 to 2.0, where 1.0 is normal playback.

[NicholasNagy]

Do we also need to do something on the android side?

[NicholasNagy]

Is it necessary to check this here? Can't we check this in the dart code so that we don't need to duplicate this code in the android side as well?

[Nisarg-18]

This is good suggestion. I'll remove the check from here and add it dart layer to avoid duplication

[NicholasNagy]

I feel like if we just return a boolean, users will have a tendency just to ignore it, as I wouldn't expect anyone to react any specific way if the setSpeed functionality doesn't work. I feel like an exception is more appropriate to throw (or rethrow in this case), so that users are aware there is an issue

[Nisarg-18]

Right, I agree, I'll update it

[Nisarg-18]

Do we also need to do something on the android side?

No, we do not need to make changes on android side. It is already implemented. BetterPlayerPlugin.java has the setSpeed case in its method channel handler, passing the "speed" parameter to the player. BetterPlayer.java implements setSpeed() which sets ExoPlayer's PlaybackParameters

Why do we have these auto generated files, and why are they being auto generated?

I'm not sure why these new files were generated but looks like these two files are automatically generated by flutter when you build the example iOS app (maybe because a change in flutter version)