[Language] make linter and type checker happy with mocking (#407)

* [Language] make linter and type checker happy with mocking

* Apply suggestions from code review
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Refactor BaseTensor class in proxy.py to implement __getitem__ and __setitem__ methods, enhancing type checking and linting compliance. Added method stubs for from_ptr and other subclasses for improved clarity and maintainability.

* Refactor type imports in proxy.py to enhance clarity and maintainability by replacing the built-in Self type with the Self type from typing_extensions.

---------
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: LeiWang1999 <leiwang1999@outlook.com>

tilelang/language/proxy.py

 """The language interface for tl programs."""
 
 from __future__ import annotations
-from typing import Optional
+from typing import Any, Optional, Sequence, SupportsIndex, TYPE_CHECKING
+from typing_extensions import Self
 
 from tvm import tir
 from tvm.tir import Var, PrimExpr
@@ -171,10 +172,57 @@ Buffer = BufferProxy()  # pylint: disable=invalid-name
 # Tensor is an alias for Buffer
 # Because when user do jit compile, the input and output will
 # be mapped with torch.Tensor.
-Tensor = TensorProxy()  # pylint: disable=invalid-name
-FragmentBuffer = FragmentBufferProxy()  # pylint: disable=invalid-name
-SharedBuffer = SharedBufferProxy()  # pylint: disable=invalid-name
-LocalBuffer = LocalBufferProxy()  # pylint: disable=invalid-name
+if TYPE_CHECKING:
+
+    class BaseTensor:
+
+        def __class_getitem__(cls, key):
+            return cls
+
+        def __getitem__(self, key) -> Any:
+            ...
+
+        def __setitem__(self, key, value) -> None:
+            ...
+
+        def __init__(
+            self,
+            shape: Sequence[SupportsIndex],
+            dtype="float32",
+            data=None,
+            strides=None,
+            elem_offset=None,
+            scope=None,  # Changed to None to use class default
+            align=None,
+            offset_factor=None,
+            buffer_type="",
+            axis_separators=None,
+        ):
+            ...
+
+        @classmethod
+        def from_ptr(cls,
+                     pointer_var: Var,
+                     shape: Sequence[PrimExpr, ...],
+                     dtype: str = "float32") -> Self:
+            ...
+
+    class Tensor(BaseTensor):
+        ...
+
+    class FragmentBuffer(BaseTensor):
+        ...
+
+    class SharedBuffer(BaseTensor):
+        ...
+
+    class LocalBuffer(BaseTensor):
+        ...
+else:
+    Tensor = TensorProxy()  # pylint: disable=invalid-name
+    FragmentBuffer = FragmentBufferProxy()  # pylint: disable=invalid-name
+    SharedBuffer = SharedBufferProxy()  # pylint: disable=invalid-name
+    LocalBuffer = LocalBufferProxy()  # pylint: disable=invalid-name
 
 
 def ptr(dtype: Optional[str] = None,