gh-106812: Small stack effect fixes (#107759)

- Generalize the syntax for the type of a stack effect to allow a trailing `*`,
  so we can declare something as e.g. `PyCodeObject *`.

- When generating assignments for stack effects,
  the type of the value on the stack should be the default (i.e., `PyObject *`)
  even when the variable copied to/from it has a different type,
  so that an appropriate cast is generated
  However, not when the variable is an array --
  then the type is taken from the variable (as it is always `PyObject **`).

Tools/cases_generator/parsing.py

@@ -252,12 +252,14 @@ class Parser(PLexer):
 
     @contextual
     def stack_effect(self) -> StackEffect | None:
-        #   IDENTIFIER [':' IDENTIFIER] ['if' '(' expression ')']
+        #   IDENTIFIER [':' IDENTIFIER [TIMES]] ['if' '(' expression ')']
         # | IDENTIFIER '[' expression ']'
         if tkn := self.expect(lx.IDENTIFIER):
             type_text = ""
             if self.expect(lx.COLON):
                 type_text = self.require(lx.IDENTIFIER).text.strip()
+                if self.expect(lx.TIMES):
+                    type_text += " *"
             cond_text = ""
             if self.expect(lx.IF):
                 self.require(lx.LPAREN)