Add #[track_caller] annotation to some panicy VM functions

This improves the error messages a bit if the the panics are triggered
in these functions

Author: eminence

numbat/src/vm.rs

@@ -515,31 +515,36 @@ impl Vm {
         self.stack.push(value);
     }
 
+    #[track_caller]
     fn pop_quantity(&mut self) -> Quantity {
         match self.pop() {
             Value::Quantity(q) => q,
             _ => panic!("Expected quantity to be on the top of the stack"),
         }
     }
 
+    #[track_caller]
     fn pop_bool(&mut self) -> bool {
         self.pop().unsafe_as_bool()
     }
 
+    #[track_caller]
     fn pop_datetime(&mut self) -> chrono::DateTime<chrono::Utc> {
         match self.pop() {
             Value::DateTime(q, _) => q,
             _ => panic!("Expected datetime to be on the top of the stack"),
         }
     }
 
+    #[track_caller]
     fn pop_string(&mut self) -> String {
         match self.pop() {
             Value::String(s) => s,
             _ => panic!("Expected string to be on the top of the stack"),
         }
     }
 
+    #[track_caller]
     fn pop(&mut self) -> Value {
         self.stack.pop().expect("stack should not be empty")
     }