Improve MemoryCatalogProvider default impl block placement (#7975)

Author: lewiszlw

datafusion/core/src/catalog/mod.rs

@@ -93,12 +93,6 @@ impl CatalogList for MemoryCatalogList {
     }
 }
 
-impl Default for MemoryCatalogProvider {
-    fn default() -> Self {
-        Self::new()
-    }
-}
-
 /// Represents a catalog, comprising a number of named schemas.
 pub trait CatalogProvider: Sync + Send {
     /// Returns the catalog provider as [`Any`]
@@ -161,6 +155,12 @@ impl MemoryCatalogProvider {
     }
 }
 
+impl Default for MemoryCatalogProvider {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl CatalogProvider for MemoryCatalogProvider {
     fn as_any(&self) -> &dyn Any {
         self