Expansion support

[daixque]

Overview

This pull request introduces a new model type for text_expansion which is related to Sparse vector query .
Until Elasticsearch and Eland 8.16, only ELSER model can be used for this query type, but with this PR and this, users can upload other sparse vector model from hugging face such as:

• naver/splade-v3-distilbert
• hotchpotch/japanese-splade-v2
• aken12/splade-japanese-v3

This is essentially the same PR as #706 but I fixed formatter issue.

Related:

• [ML] Support any tokenizers for text_expansion task elasticsearch#116935

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This pull request introduces a new model type for text expansion and refines error messaging for unsupported task types. The most important changes include the addition of the _TraceableTextExpansionModel class and updates to the _create_traceable_model method to handle this new model type.

New Model Type for Text Expansion:

• Added the _TraceableTextExpansionModel class with a _prepare_inputs method to handle text expansion tasks. (eland/ml/pytorch/transformers.py)
• Updated the _create_traceable_model method to include logic for creating a _TraceableTextExpansionModel when the task type is "text_expansion". (eland/ml/pytorch/transformers.py)

Error Messaging Improvement:

• Refined the error message in _create_traceable_model to clarify that the task type must be one of the supported task types. (eland/ml/pytorch/transformers.py)

[davidkyle]

LGTM