Fix grammar backend for tensor parallelism (#2020)

python/sglang/srt/managers/schedule_batch.py

@@ -37,6 +37,7 @@ import torch
 
 from sglang.global_config import global_config
 from sglang.srt.configs.model_config import ModelConfig
+from sglang.srt.constrained.base_grammar_backend import BaseGrammarObject
 from sglang.srt.mem_cache.base_prefix_cache import BasePrefixCache
 from sglang.srt.mem_cache.chunk_cache import ChunkCache
 from sglang.srt.mem_cache.memory_pool import BaseTokenToKVPool, ReqToTokenPool
@@ -248,7 +249,7 @@ class Req:
         self.embedding = None
 
         # Constrained decoding
-        self.grammar = None
+        self.grammar: Optional[BaseGrammarObject] = None
 
         # The number of cached tokens, that were already cached in the KV cache
         self.cached_tokens = 0