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-segment/src/distance.rs

@@ -346,8 +346,8 @@ impl Shaped {
         radius_px: f32,
     ) -> Self {
         let distance = signed_distance(coverage, width, height, threshold);
-        let distance = apply_morphology(&distance, width, height, morphology, radius_px)
-            .unwrap_or(distance);
+        let distance =
+            apply_morphology(&distance, width, height, morphology, radius_px).unwrap_or(distance);
         Self {
             distance,
             width,
@@ -403,7 +403,11 @@ mod tests {
         // Distance from the boundary, so the half-pixel comes back off to
         // compare against the centre-to-centre figures.
         let at = |x: usize, y: usize| -d[y * 5 + x] + 0.5;
-        assert!((at(1, 1) - std::f32::consts::SQRT_2).abs() < 1e-4, "{}", at(1, 1));
+        assert!(
+            (at(1, 1) - std::f32::consts::SQRT_2).abs() < 1e-4,
+            "{}",
+            at(1, 1)
+        );
         assert!((at(0, 0) - (8.0f32).sqrt()).abs() < 1e-4, "{}", at(0, 0));
         assert_eq!(at(2, 0), 2.0, "straight up is exactly two");
     }
@@ -489,7 +493,10 @@ mod tests {
         m[10 * w + 10] = 0;
 
         let before = signed_distance(&m, w, h, 128);
-        assert!(before[10 * w + 10] < 0.0, "the hole starts outside the mask");
+        assert!(
+            before[10 * w + 10] < 0.0,
+            "the hole starts outside the mask"
+        );
 
         let after = apply_morphology(&before, w, h, Morphology::Close, 2.0).expect("recomputed");
         assert!(after[10 * w + 10] >= 0.0, "closing should have filled it");