Fix a bunch of other low-hanging style lints (#36498)

- **Fix a bunch of low hanging style lints like unnecessary-return**
- **Fix single worktree violation**
- **And the rest**

Release Notes:

- N/A

crates/agent_ui/src/context_picker/completion_provider.rs

@@ -1020,7 +1020,7 @@ impl MentionCompletion {
             && line
                 .chars()
                 .nth(last_mention_start - 1)
-                .map_or(false, |c| !c.is_whitespace())
+                .is_some_and(|c| !c.is_whitespace())
         {
             return None;
         }