Use USES_TERMINAL for cpptest to show output immediately

Ninja buffers subprocess output until completion. When a test hangs,
the output is never shown, making it impossible to diagnose which test
is hanging. USES_TERMINAL gives the command direct terminal access,
bypassing ninja's buffering.

This explains why Windows CI showed test progress but Linux/macOS did
not - Windows uses MSBuild which doesn't buffer the same way.

Author: rwgk

tests/test_with_catch/CMakeLists.txt

@@ -47,7 +47,8 @@ add_custom_target(
   cpptest
   COMMAND "$<TARGET_FILE:test_with_catch>"
   DEPENDS test_with_catch
-  WORKING_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}")
+  WORKING_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
+  USES_TERMINAL)
 
 pybind11_add_module(external_module THIN_LTO external_module.cpp)
 set_target_properties(external_module PROPERTIES LIBRARY_OUTPUT_DIRECTORY