Add missing include <cstint>

Markus Blattrequested to merge
feature/fix-gcc13-2.9 into releases/2.9

GCC 13.0 complained not knowing std::uint64_t.

Cherry-picked from master

Closes #33 (closed), core/grid#169, core/localfunctions#21, extensions/dune-grid-glue#24 (closed)

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