Module: move memoized data to the intern pool

This avoids memory management bugs with the previous implementation.

src/codegen.zig

@@ -605,6 +605,9 @@ pub fn generateSymbol(
                 }
             }
         },
+        .memoized_decl,
+        .memoized_call,
+        => unreachable,
     }
     return .ok;
 }