edgedb: move Calculations into own type

dbschema/default.esdl

@@ -63,8 +63,9 @@ module default {
     required type: str {
       readonly := true;
     }
-    calculations: array<json> {
+    required multi calculations: Calculations {
       readonly := true;
+      on source delete delete target;
     }
   }
 
@@ -80,4 +81,13 @@ module default {
     }
   }
 
+  type Calculations {
+    required turn: int32 {
+      readonly := true;
+    }
+    required data: array<json> {
+      readonly := true;
+    }
+  }
+
 }