[feature] Initial block diffusion language model support (#12588)

Co-authored-by: Tiwei Bie <tiwei.btw@antgroup.com>

python/sglang/srt/model_executor/forward_batch_info.py

@@ -441,8 +441,17 @@ class ForwardBatch:
             )
             return ret
 
-        # Override the positions with spec_info
-        if (
+        # Override the positions with diffusion LLM or spec_info
+        if batch.dllm_config is not None:
+            block_size = batch.dllm_config.block_size
+            ret.positions = torch.tensor(
+                [
+                    [i for i in range(block_offset, block_offset + block_size)]
+                    for block_offset in batch.dllm_block_offsets
+                ],
+                dtype=torch.int32,
+            ).to(device, non_blocking=True)
+        elif (
             ret.spec_info is not None
             and getattr(ret.spec_info, "positions", None) is not None
         ):