[transformers] Fixed decode output cls

[romitjain]

The generation class GreedySearchDecoderOnlyOutput, SampleDecoderOnlyOutput have been deprecated from the transformers library and will be removed in the next version. I have updated it with the ouput class which is more generic.

Since the transformers version is not pinned in setup.py, this fix is crucial. The fix is backward compatible and hence won't break anything.

For example, with the current release of transformers, transformers==4.57.1, this code works:

import mamba_ssm

selective_state_update = mamba_ssm.ops.triton.selective_state_update.selective_state_update
mamba_chunk_scan_combined = mamba_ssm.ops.triton.ssd_combined.mamba_chunk_scan_combined
mamba_split_conv1d_scan_combined = mamba_ssm.ops.triton.ssd_combined.mamba_split_conv1d_scan_combined

but as soon as we install transformers from main, even the import breaks

Traceback (most recent call last):
  File "/workspace/mamba/test.py", line 1, in <module>
    import mamba_ssm
  File "/workspace/mamba/mamba_ssm/__init__.py", line 6, in <module>
    from mamba_ssm.models.mixer_seq_simple import MambaLMHeadModel
  File "/workspace/mamba/mamba_ssm/models/mixer_seq_simple.py", line 20, in <module>
    from mamba_ssm.utils.generation import GenerationMixin
  File "/workspace/mamba/mamba_ssm/utils/generation.py", line 14, in <module>
    from transformers.generation import GreedySearchDecoderOnlyOutput, SampleDecoderOnlyOutput, TextStreamer
ImportError: cannot import name 'GreedySearchDecoderOnlyOutput' from 'transformers.generation' (/workspace/transformers/src/transformers/generation/__init__.py). Did you mean: 'GenerateBeamDecoderOnlyOutput'?

After the fix in the PR, this import issue is solved.

[romitjain]

cc: @tridao

[romitjain]

Bumping up again @tridao @ko3n1g

[vasqu]

Just for reference, this is the respective PR that removed it huggingface/transformers#40998

It has been used as alias for a while now, maybe there should be a safety check to still allow this output class

[tridao]

Thanks!