[Unity][FIX] add init file to relax.backend.contrib

[Hzfengsy]

This PR adds __init__.py to relax.backend.contrib, fixing the package issue reported at mlc-ai/mlc-llm#311

cc @yzh119 @tqchen

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• cc @quic-sanirudh _{See #10317 for details}

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[masahi]

The file was removed recently to fix a circular dep problem #15001

[Hzfengsy]

@masahi Thanks for sharing. However, __init__ file is needed as setuptools will ignore files if there is no __init__ file in this folder. Maybe we need to consider an alternate way to avoid circular dep.

[masahi]

Does keeping an empty init file fix the issue? We don't want from . import cutlass (probably cublas as well) here.

[masahi]

or maybe it is fine to import cutlass as long as we are not importing partition_for_cutlass like previously.

If

from tvm.contrib.cutlass import (
    has_cutlass,
    num_cutlass_partitions,
    finalize_modules
)

doesn't get an error, I'm cool with this.

[Hzfengsy]

The empty init file is fine.

[masahi]

Here is the summary of the previous issue for reference:

• It is fine (for now) for backend/contrib/cutlass.py to depend on contrib/cutlass/build.py
• But contrib/cutlass/build.py does import relax, which transitively imports backend/contrib/cutlass.py