CMake: Centralize target linkage in source/CMakeLists.txt (#7584)

* CMake: Centralize target linkage in source/CMakeLists.txt

This refactors the CMake layout so that the top-level CMakeLists.txt is limited
to project configuration: options, feature resolution, platform/compiler setup,
and package discovery.

Target construction and linkage are centralized in source/CMakeLists.txt, which
now owns:

- the common linear-algebra dependency interface;
- optional external feature dependencies;
- the final external link closure;
- the ABACUS executable and its ordered internal target linkage;
- unit-test setup and registration of the top-level integration tests.

The final link closure is kept in one explicit location. Its order is part of
the build contract, especially for static or mixed static/shared builds:

1. internal ABACUS targets, from higher-level consumers to lower-level
   providers;
2. optional external feature libraries;
3. numerical backends and their MPI, OpenMP, compiler-runtime, and system
   dependencies.

Dependencies are therefore no longer accumulated through the legacy
`${math_libs}` path or scattered between the root CMakeLists.txt, test
directories, and setup modules. The old global OpenMP flag/link-option handling
is also removed in favour of imported targets and their usage requirements.

The top-level integration-test directory is registered only after the final
executable and its path are available. No integration-test cases are changed.

This is a structural cleanup only. It does not redesign dependency discovery or
change the current provider-selection logic for MKL, cuSOLVERMp, PEXSI, ELPA,
FFTW, ScaLAPACK, KML, or GPU dependencies, part of which need to be revised
seperately .

* Fix: Some testing target are exposed unconditionally

* Fix: Tests are built unconditionally

* Do not pass all targets to tests

* Fix: Link PEXSI properly

* Fix: Missing Torch libraries in DeePKS test

* Link Torch separately after the main dependency closure

* Add missing GTest dependency for DeePKS test support

Shared DeePKS test helpers include GoogleTest headers.

* Link DeePMD to the ESolver_DP unittest

* Resolve typo/mistake

* Attempt: Address PEXSI testing failure

* Move dependency discovery files to cmake/modules

Author: Growl1234

CMakeLists.txt

@@ -7,7 +7,7 @@
 function(setup_build_info)
     message(STATUS "Setting up build information...")
 
-    include(cmake/CollectBuildInfoVars.cmake)
+    include(${PROJECT_SOURCE_DIR}/cmake/CollectBuildInfoVars.cmake)
 
 set(BUILD_INFO_TEMPLATE "${CMAKE_SOURCE_DIR}/source/source_io/build_info.h.in")
 set(BUILD_INFO_OUTPUT   "${CMAKE_BINARY_DIR}/source/source_io/build_info.h")

cmake/BuildInfo.cmake

@@ -1,5 +1,5 @@
 # =============================================================================
-# Setup Testing Environment (GTest, CTest, AddTest function)
+# Setup unit-test dependencies and the AddTest helper
 # ==============================================================================
 
 # include_guard(GLOBAL)
@@ -12,8 +12,9 @@ macro(set_if_higher VARIABLE VALUE)
 endmacro()
 
 # Add performance test in abacus
-if(ENABLE_GOOGLEBENCH)
-  set(BUILD_TESTING ON)
+# Benchmarks are test targets; do not make them implicitly enable the full
+# unit-test tree for ordinary builds.
+if(BUILD_TESTING AND ENABLE_GOOGLEBENCH)
   find_package(benchmark HINTS ${BENCHMARK_DIR})
   if(NOT ${benchmark_FOUND})
     set(BENCHMARK_USE_BUNDLED_GTEST OFF)
@@ -38,17 +39,19 @@ endif()
       add_coverage(${UT_TARGET})
     endif()
 
-    # dependencies & link library
-    target_link_libraries(${UT_TARGET} PRIVATE ${UT_LIBS} Threads::Threads
-                          GTest::gtest_main GTest::gmock_main)
-    if(ENABLE_GOOGLEBENCH)
+    # Dependencies & link library
+    # Share the numerical/MPI/OpenMP runtime closure but not
+    # the optional feature closure of the final binary
+    target_link_libraries(${UT_TARGET} PRIVATE
+      ${UT_LIBS}
+      GTest::gtest_main
+      GTest::gmock_main
+      abacus::linalg_libs)
+    if(BUILD_TESTING AND ENABLE_GOOGLEBENCH)
       target_link_libraries(
         ${UT_TARGET} PRIVATE benchmark::benchmark)
     endif()
 
-    if(USE_OPENMP)
-      target_link_libraries(${UT_TARGET} PRIVATE OpenMP::OpenMP_CXX)
-    endif()
 
     # Link to build info if needed
     if("${UT_SOURCES}" MATCHES "parse_args.cpp")
@@ -64,8 +67,6 @@ endif()
 
 if(BUILD_TESTING)
   set_if_higher(CMAKE_CXX_STANDARD 14) # Required in orbital
-  include(CTest)
-  enable_testing()
   find_package(GTest HINTS /usr/local/lib/ ${GTEST_DIR})
   if(NOT ${GTest_FOUND})
     include(FetchContent)
@@ -77,7 +78,6 @@ if(BUILD_TESTING)
       GIT_PROGRESS TRUE)
     FetchContent_MakeAvailable(googletest)
   endif()
-  # TODO: Try the GoogleTest module.
-  # https://cmake.org/cmake/help/latest/module/GoogleTest.html
-  add_subdirectory(tests) # Contains integration tests
+  # Integration tests are registered from source/CMakeLists.txt after the
+  # final executable has been created.
 endif()