fix: fall back to HuggingFace for local encoder paths when sentence-transformers is absent

[sunnyguntuka]

Follow-up to #696. Resolves the Codex review comment on release PR #700.

Problem

In resolve_encoder, the local-path branch forced the SentenceTransformer backend unconditionally. On a pyod[huggingface]-only install (no sentence-transformers), passing a local model path raised ImportError before the existing HuggingFace fallback could run - a regression for local-path usage in HF-only environments.

Fix

The local-path branch now tries the SentenceTransformer backend first and, on ImportError, falls back to the HuggingFace backend (mirroring the existing auto-resolve pattern below it). If neither backend is available it raises a clear ImportError with install hints. Both backends load from a local directory without any Hub/network call.

Tests

Adds TestLocalPathEncoderFallback (resolver fallback control flow with _create_encoder mocked) and TestSentenceTransformerEncoderLoading (encoder local-path / remote / pre-instantiated / bad-type loading branches via a fake SentenceTransformer). All new tests run without sentence-transformers or torch installed.

No breaking API changes.

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[coveralls]

Coverage Report for CI Build 27662659891

Warning

No base build found for commit 680acf3 on development.
Coverage changes can't be calculated without a base build.
If a base build is processing, this comment will update automatically when it completes.

Coverage: 92.489%

Details

• Patch coverage: 2 uncovered changes across 1 file (91 of 93 lines covered, 97.85%).

Uncovered Changes

File	Changed	Covered	%
pyod/test/test_embedding.py	84	82	97.62%
Total (2 files)	93	91	97.85%

Coverage Regressions

Requires a base build to compare against. How to fix this →

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Coverage Stats

Relevant Lines:	20358
Covered Lines:	18829
Line Coverage:	92.49%
Coverage Strength:	3.7 hits per line

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💛 - Coveralls

[sunnyguntuka]

Hi @yzhao062 - gentle ping on this one whenever you have a moment. It's a small follow-up to #696 that closes the Codex review comment from #700: on a pyod[huggingface]-only install, a local model path now falls back to the HuggingFace backend instead of raising ImportError, with tests that run without sentence-transformers or torch. CI is green and patch coverage is ~98%. Happy to rebase or adjust anything if it'd help before merge. Thanks for all the work on PyOD!