## What changed
- Replace the ordering enum and `include_disabled` boolean with named
`ConfigLayerStack` iterators for each precedence direction.
- Keep enabled-only iteration separate from `all_layers_*` iteration, which
includes disabled layers.
- Update config consumers to use the iterator matching their precedence and
disabled-layer requirements without allocating an intermediate `Vec`.
## Testing
- Add coverage that verifies ordering and disabled-layer filtering for all four
iterators.
GitOrigin-RevId: d14df3db4a2eae80ba97cdec246bff405e6c5f3d