Generalize GridArray into Vol which allows borrowed data.

Future work: allow more orderings (only the useful ones) and migrate
away from the `GridArray` type (now a type alias).

CHANGELOG.md

@@ -36,6 +36,8 @@
         - `space::Space::draw_target()`
         - `space::SpaceTransaction::draw_target()`
 
+    - `math::GridArray` is now `math::Vol` and allows choice of the data container type.
+
     - `camera::HeadlessRenderer` now returns a custom image container type `Rendering` instead of using `image::RgbaImage`.
       (This way, no dependency on `image` is needed.)
 

all-is-cubes/src/block/evaluated.rs

@@ -526,7 +526,7 @@ impl Evoxels {
     pub(crate) fn iter_mut(&mut self) -> impl Iterator<Item = &'_ mut Evoxel> {
         match self {
             Evoxels::One(v) => core::slice::from_mut(v).iter_mut(),
-            Evoxels::Many(_, voxels) => voxels.elements_mut().iter_mut(),
+            Evoxels::Many(_, voxels) => voxels.as_linear_mut().iter_mut(),
         }
     }