fix: add missing #include <cstdint> for GCC 15 / C++23 compatibility

[jeffreyschultz]

Summary

GCC 15 and recent Clang versions with C++23 mode no longer transitively provide <cstdint> through other standard headers. This causes build failures because definitions.h uses uint32_t, int32_t, int64_t, int16_t, and uintptr_t without including the header that defines them.

Changes

• Add #include <cstdint> to include/definitions.h

Motivation

This is required to build flagser (and downstream projects like pyflagser) with:

• GCC 15+ (shipped with Ubuntu 25.04+)
• Python 3.14+ (which ships with modern toolchains)

Without this fix, the build fails with:

error: 'uint32_t' does not name a type

Testing

• Verified the fix compiles cleanly with GCC 15.2.0
• Successfully built pyflagser wheels for Python 3.14.2 on Linux x86_64

[luetge]

Thanks for the contribution, very appreciated!

[jeffreyschultz]

Sweet! Glad I could help.