Use ImmutableString in more places.

src/packages/debugging.rs

@@ -40,7 +40,7 @@ mod debugging_functions {
                 .iter()
                 .rev()
                 .filter(|crate::debugger::CallStackFrame { fn_name, args, .. }| {
-                    fn_name != "back_trace" || !args.is_empty()
+                    fn_name.as_str() != "back_trace" || !args.is_empty()
                 })
                 .map(
                     |frame @ crate::debugger::CallStackFrame {

src/packages/fn_basic.rs

@@ -27,7 +27,7 @@ mod fn_ptr_functions {
     /// ```
     #[rhai_fn(name = "name", get = "name", pure)]
     pub fn name(fn_ptr: &mut FnPtr) -> ImmutableString {
-        fn_ptr.fn_name_raw().into()
+        fn_ptr.fn_name_raw().clone()
     }
 
     /// Return `true` if the function is an anonymous function.