build(CppAD): brought in CppAD for autodiff

we need an autodiff library at some point (or we need to roll our own but I do not think that makes sense). CppAD is well tested and header only and easy to include. It is also Liscene compatible with GPL v3.0. Here we bring it in as a dependency

build-config/meson.build

@@ -8,6 +8,7 @@ subdir('opatIO')
 subdir('mpi')
 subdir('hypre')
 subdir('pybind')
+subdir('cppad')
 
 # Set the config file error handling options
 configErr = get_option('config_error_handling')
@@ -20,4 +21,4 @@ elif configErr == 'harsh'
     commonCppArgs += ['-DCONFIG_HARSH']
 endif
 
-add_project_arguments(commonCppArgs, language: 'cpp')
+add_project_arguments(commonCppArgs, language: 'cpp')