math/Imath: update to patch release 3.1.6
Patch release with miscellaneous bug/doc/build fixes.
Excerpt from release tag:
[#269] fix memory leak in V3fArrayFromBuffer [#268] Add <cstdint> for int64_t [#263] Initialize x in testRoots.cpp:solve() to suppress compiler warning [#262] Fix gcc compiler warning in testFun.cpp [#261] Test return value of extractSHRT to avoid uninitialized reference [#260] Fix example code so it compiles as is [#259] Cuda safety in several headers [#256] Fix markdown and typos in README.md [#255] Do not warn if half.h has already being included [#248] Update sphinx version
ChangeLog: https://github.com/AcademySoftwareFoundation/Imath/releases/tag/v3.1.6
MFH: 2022Q4