[V1][P/D] An native implementation of xPyD based on P2P NCCL (#18242)

Signed-off-by: Abatom <abzhonghua@gmail.com>

vllm/distributed/device_communicators/pynccl_wrapper.py

@@ -272,6 +272,14 @@ class NCCLLibrary:
             ctypes.byref(unique_id)))
         return unique_id
 
+    def unique_id_from_bytes(self, data: bytes) -> ncclUniqueId:
+        if len(data) != 128:
+            raise ValueError(
+                f"Expected 128 bytes for ncclUniqueId, got {len(data)} bytes")
+        unique_id = ncclUniqueId()
+        ctypes.memmove(ctypes.addressof(unique_id.internal), data, 128)
+        return unique_id
+
     def ncclCommInitRank(self, world_size: int, unique_id: ncclUniqueId,
                          rank: int) -> ncclComm_t:
         comm = ncclComm_t()