Fix build with modern toolchains by including <cstdint> in rasterizer_impl.h

[filippocastelli]

Summary

cuda_rasterizer/rasterizer_impl.h uses fixed-width integer types
(uint32_t, uint64_t) and std::uintptr_t, but does not explicitly
include <cstdint> (or <stdint.h>).

Older toolchains compiled successfully due to indirect includes,
but recent environments (e.g. Ubuntu 24.04 + GCC 13 + CUDA 12.6)
fail with errors such as:

• "namespace std has no member uintptr_t"
• "identifier uint32_t is undefined"
• "identifier uint64_t is undefined"

This patch adds #include <cstdint> to make the header self-contained
and restore compatibility with modern compilers.

std::uintptr_t and fixed-width integer types are defined in <cstdint>.
Relying on transitive includes is not guaranteed by the standard.

This change does not alter behavior, ABI, or performance — it only
ensures correct compilation.

Tested on

• Ubuntu 24.04
• GCC 13
• CUDA 12.6
• PyTorch CUDA extension build

Build succeeds after this change.