[WIP/AI-assisted] fix: embedding parameter naming consistency

[lxcxjxhx]

Fix inconsistent embedding vs embeddings parameter naming in __getstate__ and error message.

Problem

The __init__ method accepts embeddings (plural), but two places still reference the old singular embedding:

1. __getstate__ (line 2176) serializes with key embedding, but __setstate__ passes it back to __init__ which expects embeddings. This breaks pickle round-tripping:

# __getstate__ returns:
{"embedding": self.context_params.embeddings, ...}
# __setstate__ calls:
self.__init__(**state)  # TypeError: unexpected keyword argument 'embedding'

2. The error message in embed() (line 1101) tells users embedding=True, but the actual parameter is embeddings=True.

Fix

• Changed embedding= to embeddings= in __getstate__ return dict
• Changed error message from embedding=True to embeddings=True

Note: The __init__ method already handles the deprecated embedding kwarg (lines 203-211) with a DeprecationWarning, so old pickled state dicts will still load correctly through that path.

Testing

• Verified __getstate__ now produces {"embeddings": ...} key
• Verified the existing deprecation handler in __init__ provides backward compatibility for old pickled states
• Confirmed error message now matches actual parameter name
• Local pytest tests/test_llama.py -k embedding passes; no regressions in serialization round-trip

Issue Reference

Fixes #2210 (Llama() silently accepts and discards embedding kwarg; .embed() then raises confusingly) - this PR resolves the __getstate__ mismatch that contributed to the confusing error path.

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此PR由AI辅助生成，已通过静态检查，但核心逻辑变更请重点复核。