Format the tree the way the gate asks for it

`cargo fmt --check` is a required step and had drifted across 45 files. Most of
it arrived this week: several operations were written in parallel worktrees and
merged by hand, and a hand-merge resolves conflicts without ever running the
formatter over the result.

No behaviour changes — this is `cargo fmt --all` and nothing else, kept as its
own commit so the next reader can skip it wholesale rather than search it for
one that matters.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

core/dr-gpu/tests/masked_outputs.rs

@@ -25,7 +25,9 @@ fn ctx() -> Option<GpuContext> {
 }
 
 fn grey(ctx: &GpuContext, size: u32) -> DemosaicedImage {
-    let data: Vec<u8> = (0..size * size).flat_map(|_| [128, 128, 128, 255]).collect();
+    let data: Vec<u8> = (0..size * size)
+        .flat_map(|_| [128, 128, 128, 255])
+        .collect();
     DemosaicedImage::from_rgba8(ctx, &data, size, size).expect("upload")
 }