style(simulation): rustfmt + clippy fixes for Layer-1/heightmap code (#953 #963)

Pre-push surfaced fmt + clippy (-D warnings) failures in the new code:
- rustfmt the 6 new/changed atlas files + the bench example.
- features.rs: HashMap → BTreeMap (project bans HashMap for determinism via
  clippy disallowed_types; the bucket map is lookup-only either way).
- attractor_matching.rs: drop now-redundant .clone() on AttractorType (it
  became Copy in #953) — clippy clone_on_copy.
- drainage.rs tests: manual range → (1..=12).contains(&n).
- features.rs test: drop .clone() on Copy AttractorType.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/examples/bench_layer1.rs

@@ -50,7 +50,9 @@ fn main() {
     let o = run_layer1(&hm);
     let mut by_type: std::collections::BTreeMap<String, usize> = std::collections::BTreeMap::new();
     for a in &o.attractors {
-        *by_type.entry(format!("{:?}", a.attractor_type)).or_default() += 1;
+        *by_type
+            .entry(format!("{:?}", a.attractor_type))
+            .or_default() += 1;
     }
     println!("=== Layer-1 output for one 512×256 body ===");
     println!(