feat: bundle nvtx3 headers and remove from install export sets

nvtx3 is header-only. By installing its headers directly into cudf's
install tree, consumers find them via cudf's include path without needing
find_dependency(nvtx3) or any separate nvtx3 package.

Changes:
- get_nvtx.cmake: remove INSTALL_EXPORT_SET; propagate nvtx3_SOURCE_DIR
  to parent scope for header installation
- get_rmm.cmake: strip nvtx3::nvtx3-cpp from rmm's INTERFACE_LINK_LIBRARIES
  after fetch, preventing the absorption loop from promoting it into
  cudf's installed public interface
- CMakeLists.txt: filter nvtx3 from install-side export set merging;
  install nvtx3 headers from nvtx3_SOURCE_DIR in the DSO headers section

Author: vyasr

cpp/CMakeLists.txt

@@ -1139,9 +1139,9 @@ if(BUILD_SHARED_LIBS)
         PROPERTY "GLOBAL_TARGETS"
       )
       foreach(_pkg IN LISTS _pkg_names)
-        # Skip packages that are themselves absorbed into libcudf — they won't be installed or
-        # findable at install time.
-        if(_mode STREQUAL "install" AND _pkg IN_LIST _absorbed_deps)
+        # Skip packages that are themselves absorbed into libcudf or bundled as headers — they won't
+        # be installed as separate findable packages.
+        if(_mode STREQUAL "install" AND (_pkg IN_LIST _absorbed_deps OR _pkg STREQUAL "nvtx3"))
           continue()
         endif()
         rapids_export_package(${_mode} ${_pkg} cudf-exports GLOBAL_TARGETS ${_global_tgts})
@@ -1398,6 +1398,10 @@ if(NOT CUDF_INSTALL_LIBRARY_DEPS)
             DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
     )
   endif()
+  # nvtx3 uses SOURCE_SUBDIR c, so headers are at ${nvtx3_SOURCE_DIR}/include/nvtx3/
+  if(nvtx3_SOURCE_DIR)
+    install(DIRECTORY ${nvtx3_SOURCE_DIR}/include/nvtx3 DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
+  endif()
 endif()
 
 if(CUDF_BUILD_STREAMS_TEST_UTIL)

cpp/cmake/thirdparty/get_nvtx.cmake

@@ -5,17 +5,19 @@
 # cmake-format: on
 # =============================================================================
 
-# Need to call rapids_cpm_nvtx3 to get support for an installed version of nvtx3 and to support
-# installing it ourselves
+# Need to call rapids_cpm_nvtx3 to get the nvtx3 target available at configure time.
 function(find_and_configure_nvtx)
   include(${rapids-cmake-dir}/cpm/nvtx3.cmake)
 
-  # nvtx3 is private for cudf, but it is a public dependency of rmm. When rmm is absorbed into
-  # libcudf via whole-archive, rmm's public transitive deps (including nvtx3-cpp) are promoted into
-  # cudf's public interface. CMake's export validation requires that nvtx3-cpp be in an export set.
-  rapids_cpm_nvtx3(
-    BUILD_EXPORT_SET cudf-exports INSTALL_EXPORT_SET cudf-exports
-                                                     ${CUDF_EXCLUDE_DEPS_FROM_ALL_FLAG}
+  # nvtx3 headers are bundled directly into cudf's install tree, so we only need the build-side
+  # export set for configure-time target resolution. No INSTALL_EXPORT_SET — consumers get headers
+  # from cudf's include directory without needing find_dependency(nvtx3).
+  rapids_cpm_nvtx3(BUILD_EXPORT_SET cudf-exports ${CUDF_EXCLUDE_DEPS_FROM_ALL_FLAG})
+
+  # Propagate source dir to parent scope for header installation.
+  set(nvtx3_SOURCE_DIR
+      "${nvtx3_SOURCE_DIR}"
+      PARENT_SCOPE
   )
 
 endfunction()

cpp/cmake/thirdparty/get_rmm.cmake

@@ -21,6 +21,17 @@ function(find_and_configure_rmm BUILD_SHARED EXCLUDE_FROM_ALL)
     list(APPEND _rmm_args INSTALL_EXPORT_SET cudf-exports)
   endif()
   rapids_cpm_rmm(${_rmm_args} ${_exclude_flag} CPM_ARGS OPTIONS "BUILD_SHARED_LIBS ${BUILD_SHARED}")
+  # Remove nvtx3 from rmm's public interface. Since rmm is absorbed into libcudf via whole-archive
+  # and we bundle nvtx3 headers directly, consumers don't need the nvtx3 target. This prevents the
+  # absorption loop from promoting nvtx3 into cudf's installed interface.
+  get_target_property(_rmm_real_target rmm::rmm ALIASED_TARGET)
+  if(_rmm_real_target)
+    get_target_property(_rmm_iface_libs ${_rmm_real_target} INTERFACE_LINK_LIBRARIES)
+    if(_rmm_iface_libs)
+      list(REMOVE_ITEM _rmm_iface_libs nvtx3::nvtx3-cpp)
+      set_property(TARGET ${_rmm_real_target} PROPERTY INTERFACE_LINK_LIBRARIES ${_rmm_iface_libs})
+    endif()
+  endif()
 
   # If rmm was found as a pre-existing shared library (e.g. conda), we need find_dependency(rmm) in
   # the installed config even when EXCLUDE_FROM_ALL is set. EXCLUDE_FROM_ALL controls whether CPM-