feat: Add support for embeddings operations in langchain instrumentation

[Cirilla-zmh]

What problem do you want to solve?

Currently, embeddings operations are not automatically instrumented by loongsuite-instrumentation-langchain.

Describe the solution you'd like

• Add an instrumentation point for LangChain Embedding.
• Capture embeddings operations with genai-util.
• Add unit tests for instrumentations.

Describe alternatives you've considered

No response

Additional Context

No response

Would you like to implement a fix?

None

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