Potential Integer Overflow in mark_stacks function

There is a potential signed integer overflow in the expression:
https://github.com/python/cpython/blob/132b6bc98f47a4d897dead8635b5a50a0baee485/Objects/frameobject.c#L1365
This occurs in the loop:
https://github.com/python/cpython/blob/132b6bc98f47a4d897dead8635b5a50a0baee485/Objects/frameobject.c#L1329
len is derived from a Py_SIZE cast, and it can possibly be INT_MAX:
https://github.com/python/cpython/blob/132b6bc98f47a4d897dead8635b5a50a0baee485/Objects/frameobject.c#L1728-L1730
It means that sum can theoretically exceed INT_MAX if len is near the limit, triggering undefined behavior due to signed integer overflow.

Linked PRs

• gh-132773
• gh-132830

从 Objects/frameobject.c 中的 mark_stacks 开始，重点查看第 1329 行附近的循环和第 1365 行附近的表达式；跟踪 len 在第 1728-1730 行是如何得出的。完成的标准是：当 len 接近 INT_MAX 时，该计算不再允许 signed overflow，并且已根据链接的 PR gh-132773 和 gh-132830 检查其行为。