feat: make TweeningPlugin generic over Time

[kmorrisongr]

Closes #106

Example usage:

TweeningPlugin::<Real>::default()

TweeningPlugin::<Virtual>::default()

// Use bevy default
TweeningPlugin::<()>::default()

My use case is a tower defense game. I have very nice animations that bevy_tweening made it trivial to implement for placing towers. I use Time<Virtual> in game, because I have pause, 1x, 2x, 3x speed controls.

This works fine for wave-based logic and animations. However, it means that animations for placing towers do not play while the game is paused.

This is a breaking change, because you can no longer use a bare TweeningPlugin when adding it, you need to use TweeningPlugin::default().

I had hoped to implement more granular control, but found that animator_system applies delta_time to all tweens.

I also recognize that there might be a better way to implement this. This was implemented by Claude Opus 4.6 via VSCode Copilot. My confidence in its functionality was given by:

• tests pass
• my animations now play when the game is paused and while it is unpaused