[BE] `stdint.h`->`cstdint` (#99570)
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### <samp>🤖 Generated by Copilot at cf8834b</samp>
Updated `Generator.h` to use C++ fixed-width integers from `std` instead of C ones. This avoids potential conflicts with other libraries or platforms.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/99570
Approved by: https://github.com/huydhn, https://github.com/kit1980
