gh-106812: Small stack effect fixes

[gvanrossum]

• 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 **).

• Issue: Code generator: support variable stack effects in macros #106812