chore(deps): drop hf-classifier extra

[Pouyanpi]

Description

Drop the hf-classifier packaging extra. transformers and torch are heavy
dependencies that we do not want to declare as an installable extra; this
removes the hf-classifier extra and those two packages from the aggregate
all extra.

Coupled with docs PR #1969 (hf_classifier rail docs): its Setup section
currently shows pip install nemoguardrails[hf-classifier], which becomes
invalid once this lands. Whichever PR merges last must reconcile so the docs
show only pip install transformers torch.

AI Assistance

• No AI tools were used.
• AI tools were used; a human reviewed and can explain every change (tool: Claude Code).

Checklist

• I've read the CONTRIBUTING guidelines.
• This PR links to a triaged issue assigned to me.
• My PR title follows the project commit convention.
• I've updated the documentation if applicable. (Docs handled in docs: draft documentation for the hf_classifier rail #1969; see coupling note above.)
• I've added tests if applicable. (No behavior change; existing test_hf_classifier.py still passes.)
• I've noted any verification beyond CI and any checks I couldn't run.
• I did not update generated changelog files manually.
• I addressed all CodeRabbit, Greptile, and other review comments, or replied with why no change is needed.
• @mentions of the person or team responsible for reviewing proposed changes.

Summary by CodeRabbit

• Bug Fixes
  • Clarified the setup error message for the local HF classifier so it now points directly to the required packages to install.
  • Removed the HF classifier package from the bundled optional dependency set, simplifying installation options.

[coderabbitai]

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 2e36a78 and 40e7589.

⛔ Files ignored due to path filters (1)

• uv.lock is excluded by !**/*.lock

📒 Files selected for processing (2)

• nemoguardrails/library/hf_classifier/backends.py
• pyproject.toml

💤 Files with no reviewable changes (1)

• pyproject.toml

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📝 Walkthrough

Walkthrough

Removed the hf-classifier optional dependency extra and its transformers/torch entries from the all extra in pyproject.toml. Updated the ImportError message in backends.py to instruct installing transformers and torch directly instead of via the removed extra.

Changes

hf-classifier dependency removal

Layer / File(s)	Summary
Dependency extra and error message update pyproject.toml, nemoguardrails/library/hf_classifier/backends.py	Removed the hf-classifier extra and its transformers/torch entries from the all extra, and updated the ImportError message to suggest pip install transformers torch.

Estimated code review effort: 1 (Trivial) | ~3 minutes

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: removing the hf-classifier extra.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Test Results For Major Changes	✅ Passed	PR description includes testing info (“existing test_hf_classifier.py still passes”), and the code change is a small packaging/message edit.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch pouyanpi/drop-hf-classifier-deps

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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