Fix mesh re-allocation logic (#25259)

# Objective

Fix #18808

## Solution

Drop added meshes before allocation, in case they already had an
allocation, and generally manage slabs a little more carefully.

---------

Co-authored-by: François Mockers <francois.mockers@vleue.com>

Author: JMS55

crates/bevy_render/Cargo.toml

@@ -134,6 +134,8 @@ tracing = "0.1"
 [dev-dependencies]
 proptest = "1"
 proptest-derive = "0.8"
+# noop backend used for tests via test_utils.rs
+wgpu = { version = "30", default-features = false, features = ["noop"] }
 
 [target.'cfg(all(target_arch = "wasm32", target_feature = "atomics"))'.dependencies]
 send_wrapper = { version = "0.6.0" }

crates/bevy_render/src/lib.rs

@@ -63,6 +63,8 @@ pub mod slab_allocator;
 pub mod storage;
 pub mod sync_component;
 pub mod sync_world;
+#[cfg(test)]
+pub(crate) mod test_utils;
 pub mod texture;
 pub mod uniform;
 pub mod view;