Add <cstdint> header to nif_utils.hpp

[philss]

This change adds a new line to include this header in nif_utils.hpp.

It fixes compilation on my machine that is running with newer versions of GCC and CMake.

Details of my setup:

-- The C compiler identification is GNU 13.1.1
-- The CXX compiler identification is GNU 13.1.1
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Performing Test CXX_LINKER_SUPPORTS_VERSION_SCRIPT
-- Performing Test CXX_LINKER_SUPPORTS_VERSION_SCRIPT - Success
-- ---------------------------------------------------------------------
-- ADBC version: 0.5.1
-- 
-- Build configuration summary:
--   CMake version: 3.26.4
--   Generator: Unix Makefiles

I'm running on Fedora Linux 38 (AMD 64 bits).

[josevalim]

:green_heart: :blue_heart: :purple_heart: :yellow_heart: :heart: