Mesh picking plugin sometimes spams `Pointer<Out>` events infinitely for a stationary mouse

## Bevy version

0.16

## What you did

```rust
use bevy::{
color::palettes::css::{BLUE, GREEN, RED},
prelude::*,
};

fn main() {
App::new()
.add_plugins((DefaultPlugins, MeshPickingPlugin))
.add_systems(Startup, setup)
.add_observer(|trigger: Trigger>, names: Query<&Name>| {
info!("POINTER OUT EVENT");
info!(
"trigger.event().target: {:?} ({:?})",
trigger.event().target,
names.get(trigger.event().target)
);
info!(
"trigger.target(): {:?} ({:?}",
trigger.target(),
names.get(trigger.target())
);
})
.run();
}

fn setup(
mut commands: Commands,
mut meshes: ResMut>,
mut materials: ResMut>,
) {
commands.spawn((
Name::new("Scene"),
Transform::IDENTITY,
Visibility::Visible,
children![
hover_test_object(vec2(-150.0, 0.0), &mut meshes, &mut materials),
hover_test_object(vec2(-50.0, 0.0), &mut meshes, &mut materials),
hover_test_object(vec2(50.0, 0.0), &mut meshes, &mut materials),
hover_test_object(vec2(150.0, 0.0), &mut meshes, &mut materials),
],
));
commands.spawn((Name::new("Camera"), Camera2d));
}

pub fn hover_test_object(
pos: Vec2,
meshes: &mut ResMut>,
materials: &mut ResMut>,
) -> impl Bundle {
(
Name::new("Hover Test"),
Mesh2d(meshes.add(Rectangle::from_length(50.0))),
MeshMaterial2d(materials.add(Color::WHITE)),
Transform::from_xyz(pos.x, pos.y, 0.0),
children![
(
decoration(Color::from(GREEN), meshes, materials),
Transform::from_rotation(Quat::from_rotation_z(45_f32.to_radians()))
),
(
decoration(Color::from(BLUE), meshes, materials),
Transform::from_rotation(Quat::from_rotation_z(90_f32.to_radians()))
),
(
decoration(Color::from(RED), meshes, materials),
Transform::from_rotation(Quat::from_rotation_z(135_f32.to_radians()))
)
],
)
}

pub fn decoration(
color: Color,
meshes: &mut ResMut>,
materials: &mut ResMut>,
) -> impl Bundle {
(
Name::new("Decoration"),
Mesh2d(meshes.add(Rectangle::new(44.0, 32.0))),
MeshMaterial2d(materials.add(Color::WHITE)),
children![(
Name::new("Decoration Inner"),
Mesh2d(meshes.add(Rectangle::new(44.0, 30.0))),
MeshMaterial2d(materials.add(color)),
Transform::from_xyz(0.0, 0.0, 0.1),
)],
)
}
```

## What went wrong

Log gets spammed with `Pointer` events even when the mouse isn't moving

## Additional Information

This caused major issues for me when working on a game jam entry. I think it's related to Z-fighting, but the object is visually stable despite the erratic behavior from the picking plugin

Start by running the provided Bevy 0.16 reproduction with MeshPickingPlugin and observe Pointer events while the mouse is stationary. Trace the mesh picking and Pointer event handling from the MeshPickingPlugin entry point, including the overlapping child meshes. Done means a stationary pointer does not produce an unbounded stream of Pointer events, while pointer transitions still emit the expected events.

Written by the indexing model from the issue text.