Bevy has too many rectangle / box types

# Problem

In Bevy, there are currently:

1. https://dev-docs.bevyengine.org/bevy/a11y/accesskit/struct.Rect.html: f64, re-exported as part of our a11y work
2. https://dev-docs.bevyengine.org/bevy/math/struct.Rect.html: f32, used in UI
3. https://dev-docs.bevyengine.org/bevy/math/struct.URect.html: u32, used in UI
4. https://dev-docs.bevyengine.org/bevy/render/primitives/struct.Aabb.html: f32 3 dimensional axis-aligned bounding box, used in rendering
5. https://dev-docs.bevyengine.org/bevy/math/bounding/struct.Aabb2d.html: f32, 2 dimensional axis-aligned bounding box
6. https://dev-docs.bevyengine.org/bevy/math/bounding/struct.Aabb3d.html: f32, 3 dimensional axis-aligned bounding box
7. https://dev-docs.bevyengine.org/bevy/math/prelude/struct.Rectangle.html: f32, a mathematical primitive 2d shape w
8. https://dev-docs.bevyengine.org/bevy/math/prelude/struct.Cuboid.html: f32, a mathematical primitive 3d shape
9. https://dev-docs.bevyengine.org/bevy/ui/struct.UiRect.html: not a rectangle! Instead, used for things like padding

Please let me know if I've missed any.

We don't need this many distinct types for a rectangle! This results in user confusion, inconsistencies, duplicated API surfaces and more.

## Proposed changes

1. Don't re-export a11y types.
2. Eliminate bevy_render::Aabb in favor of the bevy_math types. Needs benchmarking.
3. Remove the `Rect` used by `bevy_ui` in favor of `Rectangle`.
4. Consider how we want to handle integer versions of geometric primitives and do so cohesively.
5. Investigate if we need distinct Aabb types, and if we do clearly document on them why just using a `Rectangle` or `Cuboid` isn't good enough.

Start by comparing the listed types in bevy_a11y/accesskit, bevy_math, bevy_render/primitives, and bevy_ui, including their documented purposes and duplicated APIs. Investigate whether bevy_render::Aabb, the UI Rect, integer primitives, and the distinct Aabb types can be consolidated without losing required behavior; benchmark the proposed render change. Done means the type set is coherent, unnecessary re-exports or duplicates are removed, and remaining distinctions are clearly documented.

Written by the indexing model from the issue text.