Remove redundant tail call resolution

The `resolve_tail_calls` function is being called twice in some
execution paths, which is unnecessary and can lead to incorrect
behavior. This commit removes the redundant calls and simplifies the
execution flow.

src/ast/vm.rs

@@ -229,7 +229,9 @@ impl VM {
         } else {
             self.unpack(&closure.parameter_node, args, &mut 0)?;
         }
-        self.eval(&closure.exec_node)
+        let result = self.eval(&closure.exec_node);
+        self.frames.pop();
+        self.resolve_tail_calls(&mut NoOpObserver, result)
     }
 
     pub fn run_with_args_observed<O: VMObserver>(
@@ -252,7 +254,9 @@ impl VM {
         } else {
             self.unpack(&closure.parameter_node, args, &mut 0)?;
         }
-        self.eval_observed(observer, &closure.exec_node)
+        let result = self.eval_observed(observer, &closure.exec_node);
+        self.frames.pop();
+        self.resolve_tail_calls(observer, result)
     }
 
     pub fn run_with_observer<O: VMObserver>(