Replace int64_t with a size type in python_list.h when applicable (#101922)
Potentially fixes the second issue described in #87159.
In python_list.h, `int64_t` is used when `diff_type` is better suited. On 32 bit systems, int64_t isn't a proper signed size type, which may cause the compilation error described in #87159.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/101922
Approved by: https://github.com/Skylion007
