improve lifetime annotation in bot

fish/src/bot.rs

@@ -103,7 +103,7 @@ impl SegmentedAStar {
         }
     }
 
-    fn expand(&mut self, arena: &Arena) -> Result<&Node, ShouldSelect> {
+    fn expand<'a>(&mut self, arena: &'a Arena) -> Result<&'a Node, ShouldSelect> {
         let open_set = self.open.get_mut(self.depth);
         let cand = open_set.map_or(None, |set| set.pop()).ok_or(ShouldSelect)?;
         let cand = unsafe { cand.0.as_node() };