Add multidual_eigen: Eigen integration for dual<T,N>

Michael Teschrequested to merge
feature/multidual-eigen into master

Summary

  • New header duals/multidual_eigen — provides NumTraits, ScalarBinaryOpTraits, and matrix-level rpart/dpart/dconj functors for dual<T,N>.
  • Fix C++20 build error: remove illegal std::is_compound specializations from duals/dual and duals/multidual.
  • Replace local NumTraits shim in bench_expm_deriv.cpp with the proper header.

Test plan

  • 446/446 tests pass
  • expm benchmarks build and run with multidual_eigen (both old and new targets)
  • equivalency tests pass

Merge request reports