Refactor product optimization methods into a specific module.

misc/test/src/C++/unit/faust_transform_omp_mul.cpp.in

src/algorithm/factorization/faust_Palm4MSA.hpp

src/faust_linear_operator/CPU/faust_Transform.h

src/faust_linear_operator/CPU/faust_Transform.hpp

src/faust_linear_operator/CPU/faust_TransformHelper.h

src/faust_linear_operator/CPU/faust_TransformHelper.hpp

src/faust_linear_operator/CPU/faust_linear_algebra.h

src/faust_linear_operator/CPU/faust_linear_algebra.hpp

src/faust_linear_operator/CPU/faust_prod_opt.h

src/faust_linear_operator/CPU/faust_prod_opt.hpp