clear animation evaluator stack (#21118)

# Objective

A large complex animation (2642 curves over 62 joints) causes serious
residual noise on joints after it stops playing. here i start the
animation then quickly cancel it:


https://github.com/user-attachments/assets/9552d69e-bb10-400f-94a6-c93d301c689b

this also seems to affect entities that are animated, but not by the
player that fires the large animation, which is really bizarre (here i
do not cancel it):


https://github.com/user-attachments/assets/a0d99df5-f53d-4ff0-9cf1-87a0e78b8abd


## Solution

debugging i found that the curve evaluator stack is growing unbounded
while the complex animation is playing (100k items after a second or
two) and is not cleared after the animation is stopped / replaced, so i
tried clearing the evaluator stack and that seems to fix it.

i have no idea if this fix is sensible or if the root of the issue is
elsewhere. i don't see any knockon ill-effects but can't be sure there
aren't any. i do not understand this code at all and it's hard to get a
clear picture of what it's trying to do, so hopefully somebody who does
understand it can diagnose better.

i attached the gltf containing the animation that causes the issue but i
can't give a simple repro - in my code i have to retarget the animation
onto an avatar which isn't included in the animation gltf (i can provide
an example for that if anybody wants it).


[bafybeicoja22tkr2rxpccmwh74yehnurgolias77reztd2kuhtvsn2luue.glb.zip](https://github.com/user-attachments/files/22408365/bafybeicoja22tkr2rxpccmwh74yehnurgolias77reztd2kuhtvsn2luue.glb.zip)


## Testing

no

Co-authored-by: Alice Cecile <[email protected]>

Author: robtfm

crates/bevy_animation/src/animation_curves.rs

@@ -416,6 +416,7 @@ impl<A: Animatable> AnimationCurveEvaluator for AnimatableCurveEvaluator<A> {
             .pop()
             .ok_or_else(inconsistent::<AnimatableCurveEvaluator<A>>)?
             .value;
+        self.evaluator.stack.clear();
         Ok(())
     }
 }