feat: implement assert

nix-js/src/runtime.rs

@@ -353,7 +353,7 @@ fn to_value<'a, 'b>(val: v8::Local<'a, v8::Value>, ctx: &RuntimeContext<'a, 'b>)
                 .collect();
             Value::AttrSet(AttrSet::new(attrs))
         }
-        _ => todo!("{}", val.type_repr()),
+        _ => unimplemented!("can not convert {} to NixValue", val.type_repr()),
     }
 }