feat(compiler): copy cpp optim lib into output lib dir

this makes sure it will be installed as part of the compiler, as needed
currently by the rust bindings

compilers/concrete-compiler/compiler/CMakeLists.txt

@@ -82,7 +82,7 @@ ExternalProject_Add(
   BUILD_ALWAYS true
   BUILD_COMMAND cargo build -p concrete-optimizer-cpp --profile release
   BINARY_DIR "${CONCRETE_OPTIMIZER_DIR}"
-  INSTALL_COMMAND ""
+  INSTALL_COMMAND cp ${CONCRETE_OPTIMIZER_STATIC_LIB} ${CMAKE_LIBRARY_OUTPUT_DIRECTORY}
   LOG_BUILD ON
   LOG_OUTPUT_ON_FAILURE ON)