docs(mta): suppress invalid sequence syntax warning (#870)

## Summary
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this proposed code change. --->
According to [PEP-257](https://peps.python.org/pep-0257/):

> For consistency, always use """triple double quotes""" around
docstrings. Use r"""raw triple double quotes""" if you use any
backslashes in your docstrings.

Fix #866 and a coding style issue in setup.py

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## Details
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## Testing Done
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---------

Signed-off-by: Tcc0403 <[email protected]>

Author: Tcc0403

setup.py

@@ -109,5 +109,5 @@ def get_platform() -> Literal["cuda", "rocm", "cpu", "xpu"]:
         "Topic :: Software Development :: Libraries :: Python Modules",
         "License :: OSI Approved :: BSD-2-Clause Software License",
         "Operating System :: OS Independent",
-    ]
+    ],
 )

src/liger_kernel/transformers/multi_token_attention.py

@@ -9,7 +9,7 @@
 
 
 class LigerMultiTokenAttention(nn.Module):
-    """
+    r"""
     Multi-Token Attention:
         out = mask_{0}(conv2d(softmax(mask_{-\inf}(scores))))