[Misc] Set default value of seed to None (#14274)

Signed-off-by: மனோஜ்குமார் பழனிச்சாமி <smartmanoj42857@gmail.com>

vllm/engine/arg_utils.py

@@ -104,7 +104,7 @@ class EngineArgs:
     config_format: ConfigFormat = ConfigFormat.AUTO
     dtype: str = 'auto'
     kv_cache_dtype: str = 'auto'
-    seed: int = 0
+    seed: Optional[int] = None
     max_model_len: Optional[int] = None
     # Note: Specifying a custom executor backend by passing a class
     # is intended for expert use only. The API may change without