[Feature] Option to save model weights to CPU when memory saver mode is enabled (#10873)

Co-authored-by: molocule <34072934+molocule@users.noreply.github.com>

python/sglang/srt/server_args.py

@@ -400,6 +400,7 @@ class ServerArgs:
     num_continuous_decode_steps: int = 1
     delete_ckpt_after_loading: bool = False
     enable_memory_saver: bool = False
+    enable_weights_cpu_backup: bool = False
     allow_auto_truncate: bool = False
     enable_custom_logit_processor: bool = False
     flashinfer_mla_disable_ragged: bool = False
@@ -2541,6 +2542,11 @@ class ServerArgs:
             action="store_true",
             help="Allow saving memory using release_memory_occupation and resume_memory_occupation",
         )
+        parser.add_argument(
+            "--enable-weights-cpu-backup",
+            action="store_true",
+            help="Save model weights to CPU memory during release_weights_occupation and resume_weights_occupation",
+        )
         parser.add_argument(
             "--allow-auto-truncate",
             action="store_true",