fix(python-sdk): restrict transformers version for python 3.9 compat

[liferoad]

Versions 4.55.0+ use Python 3.10+ union syntax which causes TypeError on Python 3.9

apache_beam/ml/transforms/embeddings/huggingface.py:37: in <module> |  
-- | --
from sentence_transformers import SentenceTransformer |  
../../build/gradleenv/1922375555/lib/python3.9/site-packages/sentence_transformers/__init__.py:15: in <module> |  
from sentence_transformers.cross_encoder import ( |  
../../build/gradleenv/1922375555/lib/python3.9/site-packages/sentence_transformers/cross_encoder/__init__.py:5: in <module> |  
from .trainer import CrossEncoderTrainer |  
../../build/gradleenv/1922375555/lib/python3.9/site-packages/sentence_transformers/cross_encoder/trainer.py:22: in <module> |  
from sentence_transformers.trainer import SentenceTransformerTrainer |  
../../build/gradleenv/1922375555/lib/python3.9/site-packages/sentence_transformers/trainer.py:16: in <module> |  
from transformers import EvalPrediction, PreTrainedTokenizerBase, Trainer, TrainerCallback |  
<frozen importlib._bootstrap>:1055: in _handle_fromlist |  
??? |  
../../build/gradleenv/1922375555/lib/python3.9/site-packages/transformers/utils/import_utils.py:2317: in __getattr__ |  
module = self._get_module(self._class_to_module[name]) |  
../../build/gradleenv/1922375555/lib/python3.9/site-packages/transformers/utils/import_utils.py:2347: in _get_module |  
raise e |  
../../build/gradleenv/1922375555/lib/python3.9/site-packages/transformers/utils/import_utils.py:2345: in _get_module |  
return importlib.import_module("." + module_name, self.__name__) |  
/opt/hostedtoolcache/Python/3.9.22/x64/lib/python3.9/importlib/__init__.py:127: in import_module |  
return _bootstrap._gcd_import(name[level:], package, level) |  
../../build/gradleenv/1922375555/lib/python3.9/site-packages/transformers/trainer.py:311: in <module> |  
class Trainer: |  
../../build/gradleenv/1922375555/lib/python3.9/site-packages/transformers/trainer.py:5593: in Trainer |  
def _get_num_items_in_batch(self, batch_samples: list, device: torch.device) -> int \| None: |  
E   TypeError: unsupported operand type(s) for \|: 'type' and 'NoneType' |  
 

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Tested: https://github.com/apache/beam/actions/runs/18237181501/job/51934437687?pr=36385 is green now.

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[gemini-code-assist]

Summary of Changes

Hello @liferoad, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical compatibility issue within the Python SDK related to the transformers library. It implements a conditional version restriction for transformers to ensure that users running Python 3.9 do not encounter TypeError exceptions caused by newer union type syntax introduced in transformers versions 4.55.0 and later, which are only compatible with Python 3.10 and above. This change maintains broader Python version support for the SDK while allowing newer Python environments to utilize the latest compatible transformers versions.

Highlights

• Python 3.9 Compatibility: The transformers library version is now conditionally restricted for Python 3.9 environments. Specifically, transformers versions 4.55.0 and above utilize Python 3.10+ union syntax (int | None), which leads to TypeError on Python 3.9. To prevent this, Python 3.9 users will now install transformers versions less than 4.55.0.
• Conditional Dependency: A conditional dependency has been introduced in setup.py for the transformers package. For Python versions less than 3.10, the dependency is set to transformers>=4.28.0,<4.55.0. For Python 3.10 and above, the dependency remains transformers>=4.28.0,<4.56.0.

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