Sprite clipRect improvements

[Sword352]

• Don't round clipRect to ensure smooth clipping no matter the scale
• Put clipRect back into the pool when the sprite is destroyed

Here is a sample demonstrating the visual changes of this pull request:

package;

import flixel.FlxG;
import flixel.FlxSprite;
import flixel.FlxState;

class PlayState extends FlxState
{
	var sprite:FlxSprite;
	var speed:Float = 1 / 4;
	var total:Float = 0;

	override function create():Void
	{
		super.create();

		sprite = new FlxSprite();
		sprite.loadGraphic("flixel/images/logo/default.png");
		sprite.scale.set(12, 12);
		sprite.updateHitbox();
		sprite.screenCenter();
		add(sprite);

		sprite.clipRect = flixel.math.FlxRect.get(0, 0, sprite.frameWidth, sprite.frameHeight);
	}

	function updateClipRect(increment:Float):Void
	{
		total += increment;
		sprite.clipRect.y = total;
		sprite.clipRect = sprite.clipRect;
	}

	override function update(elapsed:Float):Void
	{
		super.update(elapsed);

		if (FlxG.keys.pressed.DOWN)
			updateClipRect(sprite.frameHeight * speed * elapsed);

		if (FlxG.keys.pressed.UP)
			updateClipRect(sprite.frameHeight * -speed * elapsed);
	}
}

Without this change, the sprite from the sample clips in "chuncks"
https://github.com/user-attachments/assets/36343c09-b20e-4c6a-80f0-d219225f2620

With this change, the sprite now clips much smoother
https://github.com/user-attachments/assets/304f8b45-75c4-4cfe-bd1b-3f0a01b07c20