Fix installed include path export

Export both installed include roots so downstream consumers can use the public cddp-cpp header layout while existing internal quoted includes keep working. Strengthen the package smoke test to compile against installed cddp-cpp headers directly.

Author: astomodynamics

CMakeLists.txt

@@ -186,6 +186,7 @@ endif()
 
 target_include_directories(${PROJECT_NAME} PUBLIC
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include/cddp-cpp>
+  $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
   $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/cddp-cpp>
 )
 

tests/package_smoke/main.cpp

@@ -1,3 +1,8 @@
-#include "cddp.hpp"
+#include <cddp-cpp/cddp.hpp>
+#include <cddp-cpp/cddp_core/helper.hpp>
 
-int main() { return 0; }
+int main() {
+  const auto finite = cddp::finite_difference_jacobian(
+      [](const Eigen::VectorXd &x) { return x; }, Eigen::VectorXd::Zero(1));
+  return finite.rows() == 1 ? 0 : 1;
+}