[XPU] keep generator state of sycl kernel align with pytorch (#41771)

Signed-off-by: Yan Ma <yan.ma@intel.com>
Co-authored-by: Qiming Zhang <qiming1.zhang@intel.com>
Co-authored-by: Kunshang Ji <kunshang.ji@intel.com>

vllm/v1/sample/ops/topk_topp_sampler.py

@@ -289,6 +289,11 @@ class TopKTopPSampler(nn.Module):
         torch.ops.vllm.xpu_topk_topp_sampler(
             random_sampled, logits_to_return, logits, k, p, self.logprobs_mode, seeds
         )
+        # The custom XPU sampler kernel consumes RNG values internally, so advance
+        # the default generator's offset to keep future draws deterministic.
+        offset += logits.numel()
+        state.view(torch.int64)[1] = offset
+        generator.set_state(state)
         return random_sampled, logits_to_return