[Inference/SpecDec] Add Basic Drafter Model Container (#5405)

* [Infer/Fix] Fix Dependency in test - RMSNorm kernel (#5399)

fix dependency in pytest

* add drafter model container (basic ver)

colossalai/inference/spec/struct.py

@@ -0,0 +1,29 @@
+from dataclasses import dataclass
+from typing import Optional, Tuple
+
+import torch
+
+
+@dataclass
+class DrafterOutput:
+    """
+    Dataclass for drafter model outputs.
+
+    Args:
+        speculated_length (int): Speculated length of the output sequence
+            It is always less than or equal to spec_num during drafter's speculation process
+        logits (torch.FloatTensor): Logits of the output sequence
+        next_tokens (torch.Tensor): Next token ids
+        past_key_values (Optional[Tuple[Tuple[torch.FloatTensor]]]): Past key values of the output sequence
+    """
+
+    speculated_length: int = None
+    logits: torch.FloatTensor = None
+    next_tokens: torch.Tensor = None
+    past_key_values: Optional[Tuple[Tuple[torch.FloatTensor]]] = None
+
+    def __post_init__(self):
+        assert self.speculated_length is not None and self.speculated_length >= 0
+        if self.past_key_values is not None:
+            assert isinstance(self.past_key_values, tuple), "Past key values should be a tuple"
+            assert all([isinstance(past_key_value, tuple) for past_key_value in self.past_key_values])