refactor(sim): resolve clippy pedantic lints

- Replace signed coordinate round-trips with checked offset helpers
- Use From/try_from conversions and clamp helpers in the edit parser
- Isolate exact RNG, noise and day-fraction float casts in documented helpers
- Split long functions (validate, world creation, apply, state_json, tick_person)
- Pass run_sim shared state by reference and tidy remaining style lints

Simulation behaviour and RNG sequences are unchanged.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/main.rs

@@ -57,10 +57,10 @@ fn run_sim(
         snapshot,
     }: SimStart,
     mut rx: mpsc::UnboundedReceiver<Msg>,
-    terrain: Arc<Mutex<String>>,
-    script: Arc<Mutex<String>>,
-    state_tx: watch::Sender<Arc<str>>,
-    snapshot_tx: watch::Sender<Option<String>>,
+    terrain: &Mutex<String>,
+    script: &Mutex<String>,
+    state_tx: &watch::Sender<Arc<str>>,
+    snapshot_tx: &watch::Sender<Option<String>>,
 ) {
     let mut world = match snapshot {
         Some(snapshot) => World::from_snapshot_with_script(&snapshot, seed, sim_script)
@@ -235,7 +235,7 @@ async fn client(mut socket: WebSocket, app: App) {
                     Some(Ok(Message::Text(t))) if t.len() <= 256 => {
                         let _ = app.tx.send(Msg::Edit(t.as_str().to_owned()));
                     }
-                    Some(Ok(Message::Close(_))) | Some(Err(_)) | None => return,
+                    Some(Ok(Message::Close(_)) | Err(_)) | None => return,
                     _ => {}
                 },
             }
@@ -309,11 +309,11 @@ async fn main() {
                     snapshot: saved_snapshot,
                 },
                 rx,
-                terrain_buf,
-                script,
-                state_tx,
-                snapshot_tx,
-            )
+                &terrain_buf,
+                &script,
+                &state_tx,
+                &snapshot_tx,
+            );
         });
     }