Support compiling with GCC 13

[JeanChristopheMorinPerso]

When compiling with GCC 13, we get errors like this:

In file included from /home/jcmorin/jcmenv/aswf/OpenTimelineIO/src/opentime/rationalTime.cpp:4:
/home/jcmorin/jcmenv/aswf/OpenTimelineIO/src/opentime/rationalTime.h: In function ‘constexpr double opentime::v1_0::fabs(double)’:
/home/jcmorin/jcmenv/aswf/OpenTimelineIO/src/opentime/rationalTime.h:27:9: error: ‘uint64_t’ does not name a type
   27 |         uint64_t i;
      |         ^~~~~~~~
/home/jcmorin/jcmenv/aswf/OpenTimelineIO/src/opentime/rationalTime.h:10:1: note: ‘uint64_t’ is defined in header ‘<cstdint>’; did you forget to ‘#include <cstdint>’?
    9 | #include <limits>
  +++ |+#include <cstdint>
   10 | #include <string>
/home/jcmorin/jcmenv/aswf/OpenTimelineIO/src/opentime/rationalTime.h:29:10: error: ‘union opentime::v1_0::fabs(double)::<unnamed>’ has no member named ‘i’
   29 |     bits.i &= std::numeric_limits<uint64_t>::max() / 2;
      |          ^
/home/jcmorin/jcmenv/aswf/OpenTimelineIO/src/opentime/rationalTime.h:29:35: error: ‘uint64_t’ was not declared in this scope
   29 |     bits.i &= std::numeric_limits<uint64_t>::max() / 2;
      |                                   ^~~~~~~~
/home/jcmorin/jcmenv/aswf/OpenTimelineIO/src/opentime/rationalTime.h:29:35: note: ‘uint64_t’ is defined in header ‘<cstdint>’; did you forget to ‘#include <cstdint>’?
/home/jcmorin/jcmenv/aswf/OpenTimelineIO/src/opentime/rationalTime.h:29:43: error: template argument 1 is invalid
   29 |     bits.i &= std::numeric_limits<uint64_t>::max() / 2;

Like the note says, we need to include cstdint. This is also documented in https://gcc.gnu.org/gcc-13/porting_to.html#header-dep-changes.

[codecov-commenter]

Codecov Report

Merging #1605 (589f6b7) into main (23ff3f9) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1605   +/-   ##
=======================================
  Coverage   79.91%   79.91%           
=======================================
  Files         197      197           
  Lines       21731    21731           
  Branches     4339     4339           
=======================================
  Hits        17366    17366           
  Misses       2213     2213           
  Partials     2152     2152           

Flag	Coverage Δ
py-unittests	79.91% <ø> (ø)

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Impacted Files	Coverage Δ
src/opentime/rationalTime.h	94.31% <ø> (ø)

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