Support xccl distributed backend

Starting from `torch>=2.7` XCCL distributed backend is available
for XPU devices (requires torch built with `USE_XCCL=1`).

This commit is verified on Intel Data Center GPU Max with Bloom:
```
text-generation-launcher --sharded true --num-shard 2 \
  --model-id bigscience/bloom-560m
```

Signed-off-by: Dmitry Rogozhkin <dmitry.v.rogozhkin@intel.com>

server/text_generation_server/utils/dist.py

@@ -3,6 +3,7 @@ import torch
 from torch.distributed import ProcessGroup
 from datetime import timedelta
 from loguru import logger
+from packaging import version
 from text_generation_server.utils.import_utils import SYSTEM
 
 # Tensor Parallelism settings
@@ -45,6 +46,12 @@ class FakeGroup(ProcessGroup):
         return self._rank
 
 
+def _is_xccl_available():
+    if version.parse(torch.__version__).release >= version.parse("2.7").release:
+        return torch.distributed.distributed_c10d.is_xccl_available()
+    return False
+
+
 def initialize_torch_distributed():
     if torch.cuda.is_available():
         from torch.distributed import ProcessGroupNCCL
@@ -54,11 +61,20 @@ def initialize_torch_distributed():
         device = RANK % torch.cuda.device_count()
         torch.cuda.set_device(device)
         torch.cuda.set_per_process_memory_fraction(MEMORY_FRACTION, device)
+        device = "cuda"
         backend = "nccl"
         options = ProcessGroupNCCL.Options()
         options.is_high_priority_stream = True
         options._timeout = timedelta(seconds=120)
+    elif SYSTEM == "xpu" and _is_xccl_available():
+        assert WORLD_SIZE <= torch.xpu.device_count(), "Each process is one gpu"
+        device = RANK % torch.xpu.device_count()
+        torch.xpu.set_device(device)
+        device = "xpu"
+        backend = "xccl"
+        options = None
     else:
+        device = None
         backend = "gloo"
         options = None
 
@@ -81,7 +97,8 @@ def initialize_torch_distributed():
                     pg_options=options,
                 )
             else:
-                device = torch.device(f"cuda:{RANK}")
+                if device:
+                    device = torch.device(f"{device}:{RANK}")
                 torch.distributed.init_process_group(
                     backend=backend,
                     world_size=WORLD_SIZE,
@@ -90,6 +107,7 @@ def initialize_torch_distributed():
                     pg_options=options,
                     device_id=device,
                 )
+                logger.info(f"torch.distributed initialized with {backend} backend for rank {RANK}")
         else:
             logger.warning("torch.distributed is already initialized.")