adding the missing header for uint8_t

In file included from AlgoHex/external/OpenVolumeMesh/src/OpenVolumeMesh/IO/detail/WriteBuffer.cc:1:
AlgoHex/external/OpenVolumeMesh/src/OpenVolumeMesh/IO/detail/WriteBuffer.hh:12:17: error: ‘uint8_t’ was not declared in this scope
   12 |     std::vector<uint8_t> vec() const;;
      |                 ^~~~~~~
AlgoHex/external/OpenVolumeMesh/src/OpenVolumeMesh/IO/detail/WriteBuffer.hh:6:1: note: ‘uint8_t’ is defined in header ‘<cstdint>’; did you forget to ‘#include <cstdint>’?
    5 | #include <vector>
  +++ |+#include <cstdint>