fix: resolve PR comments

src/common/meta/src/key/table_route.rs

@@ -40,6 +40,7 @@ impl TableRouteKey {
 #[derive(Debug, PartialEq, Serialize, Deserialize, Clone)]
 pub enum TableRouteValue {
     Mito(MitoTableRouteValue),
+    File(FileTableRouteValue),
     Metrics(MetricsTableRouteValue),
 }
 
@@ -49,6 +50,10 @@ pub struct MitoTableRouteValue {
     version: u64,
 }
 
+// TODO(LFC): Make file engine table use its own table route.
+#[derive(Debug, PartialEq, Serialize, Deserialize, Clone)]
+pub struct FileTableRouteValue;
+
 #[derive(Debug, PartialEq, Serialize, Deserialize, Clone)]
 pub struct MetricsTableRouteValue {
     // TODO(LFC): Add table route for MetricsEngine table.
@@ -88,6 +93,10 @@ impl TableRouteValue {
             .cloned()
     }
 
+    /// Gets the [RegionRoute]s of this table route.
+    ///
+    /// # Panics
+    /// The engine type of this table is not "`Mito`".
     pub fn region_routes(&self) -> &Vec<RegionRoute> {
         &self.mito_table_route().region_routes
     }