Add CutlassSemiSparseFp8Tensor

Summary:
Moving float8 cutlass sparse layout into its own class:
https://github.com/pytorch/ao/blob/main/torchao/dtypes/floatx/cutlass_semi_sparse_layout.py

Differential Revision: D84467190

Author: bbeckca

torchao/quantization/quantize_/workflows/float8/cutlass_semi_sparse_fp8_tensor.py

@@ -0,0 +1,56 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD 3-Clause license found in the
+# LICENSE file in the root directory of this source tree.
+import torch
+from torchao.utils import TorchAOBaseTensor
+
+__all__ = ["CutlassSemiSparseFp8Tensor"]
+aten = torch.ops.aten
+
+class CutlassSemiSparseFp8Tensor(TorchAOBaseTensor):
+    tensor_data_names = ["sparse", "scale", "meta"]
+
+    def __new__(
+        cls,
+        sparse: torch.Tensor,
+        meta: torch.Tensor,
+        scale: torch.Tensor,
+    ):
+        kwargs = {}
+        kwargs["device"] = sparse.device
+        kwargs["dtype"] = scale.dtype
+        kwargs["requires_grad"] = False
+        shape = (sparse.shape[0], 2 * sparse.shape[-1])
+        return torch.Tensor._make_wrapper_subclass(cls, shape, **kwargs)  # type: ignore[attr-defined]
+
+
+    def __init__(
+        self,
+        sparse: torch.Tensor,
+        meta: torch.Tensor,
+        scale: torch.Tensor,
+    ):
+        super().__init__()
+        self.sparse = sparse
+        self.meta = meta
+        self.scale = scale
+
+    def _quantization_type(self):
+        return f"shape={self.shape}, device={self.device}, dtype={self.dtype}"
+
+    
+    @classmethod
+    def from_hp(
+        ):
+        raise NotImplementedError("CutlassSemiSparseFp8Tensor.from_hp is not implemented yet")
+
+    
+implements = CutlassSemiSparseFp8Tensor.implements
+implements_torch_function = CutlassSemiSparseFp8Tensor.implements_torch_function
+
+CutlassSemiSparseFp8Tensor.__module__ = "torchao.quantization"
+
+# Allow a model with CutlassSemiSparseFp8Tensor weights to be loaded with `weights_only=True`
+torch.serialization.add_safe_globals([CutlassSemiSparseFp8Tensor])