- tested with eigen 3.3.7 & 3.3.8.
- rearrange how we're (illegally using/abusing) std:: by moving many implementation details
  into duals::detail tricks - makes everything work with LIBCPP on osx now (as of Sequoia 15.2).
- upgrade google test & benchmark libraries.
- update to more modern cmake, at least 3.14 required now.
- dont try to use Eigen's .exp() with duals, not supported.

Known Issues
- fmt library support is very out of date - should update to support std::format.
- coverage is not working.
- SSE/AVX not working - open to fixes but dont have a machine to test on at the moment.