Feat(psi): add PsiStorageMode and device_memory_mode for GPU k-point paging

- Add PsiStorageMode enum (ALL_GPU, ALL_CPU, PAGED_GPU) to psi namespace
- Add paging interface: load_k_to_gpu, store_k_from_gpu, ensure_k_on_gpu
- Modify resize() to allocate CPU storage + single-k GPU buffer in PAGED_GPU mode
- Create psi_paging.cpp with paging method implementations
- Add device_memory_mode INPUT parameter (''/full_gpu/paged)
- Add device_memory_mode reading in read_input_item_system.cpp

Author: dyzheng

source/source_io/module_parameter/input_parameter.h

@@ -70,6 +70,7 @@ struct Input_para
     double min_dist_coef = 0.2;                     ///< allowed minimum distance between two atoms
 
     std::string device = "cpu";
+    std::string device_memory_mode = "";    ///< GPU memory mode: "" (auto), "full_gpu" (all on GPU), "paged" (CPU storage + k-point paging)
     std::string precision = "double";
     std::string gint_precision = "double";
     bool timer_enable_nvtx = false;

source/source_io/module_parameter/read_input_item_system.cpp

@@ -743,6 +743,28 @@ Available options are:
         };
         this->add_item(item);
     }
+    {
+        Input_Item item("device_memory_mode");
+        item.annotation = "GPU memory strategy for wavefunction storage";
+        item.category = "System variables";
+        item.type = "String";
+        item.description = R"(Controls GPU memory strategy for wavefunction storage.
+* "" (empty/auto): Automatic selection based on system size.
+* "full_gpu": All wavefunction data resides on GPU (default behavior).
+* "paged": CPU storage with single k-point paging to GPU, reduces GPU memory at the cost of transfer overhead.
+
+Only relevant when device=gpu and basis_type=pw.)";
+        item.default_value = "";
+        read_sync_string(input.device_memory_mode);
+        item.check_value = [](const Input_Item& item, const Parameter& para) {
+            const std::vector<std::string> avail_list = {"", "full_gpu", "paged"};
+            if (std::find(avail_list.begin(), avail_list.end(), para.input.device_memory_mode) == avail_list.end())
+            {
+                ModuleBase::WARNING_QUIT("ReadInput", "device_memory_mode must be empty, full_gpu, or paged.");
+            }
+        };
+        this->add_item(item);
+    }
     {
         Input_Item item("precision");
         item.annotation = "the computing precision for ABACUS";

source/source_psi/CMakeLists.txt

@@ -2,6 +2,7 @@ add_library(
     psi
     OBJECT
     psi.cpp
+    psi_paging.cpp
 )
 
 add_library(