refactor: set do_sample=True if a seed is set on HF backends

[psschwei]

Pull Request

Issue

Fixes #40

Description

HuggingFace backends silently ignored seed (and warned but ignored temperature) because transformers defaults to greedy decoding (do_sample=False). This change forces do_sample=True in _make_backend_specific_and_remove whenever a SEED or non-zero TEMPERATURE is set and the caller hasn't explicitly chosen do_sample, fixing all four HF generate paths in one place.

Testing

• Tests added to the respective file if code was changed
• New code has 100% coverage if code was added
• Ensure existing tests and github automation passes (a maintainer will kick off the github automation when the rest of the PR is populated)

Attribution

• AI coding assistants used

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Adding a new component, requirement, sampling strategy, or tool?

If your PR adds or modifies one of the types below, check the matching box. A checklist of type-specific review items will be posted as a comment.

• Component
• Requirement
• Sampling Strategy
• Tool

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