Specified the minimum apple-clang version to support `std::format` to 16
for _connanfile.py_. Xcode 16 does include the `<format>` header but
does not seem to have the __cpp_lib_format compatibility macro defined
so a similar override was needed as we had for Clang 17.
To be able to use `std::format` with Xcode 16 I had to pass
`-DMP_UNITS_API_STD_FORMAT=AUTO` when calling `cmake`. Is this expected
or is this a sign I missed something in my changes to _CMakeLists.txt_?
Roth Michaels
43729c6190