(Data): Small extensions to core data interfaces.

Add `LEQ` condition type.
Ensure that batch updates don't fire with nothing to update.
Add `cast_row` to `update_many` for handling typed `NULL`s.

bot/data/interfaces.py

@@ -113,7 +113,8 @@ class Row:
         try:
             yield self._pending
         finally:
-            self.update(**self._pending)
+            if self._pending:
+                self.update(**self._pending)
             self._pending = None
 
     def _refresh(self):