Adding support for DashScopeEmbeddings to handle Aliyun embedding models

[ZZH-qwq]

This fix ensures proper initialization of Aliyun's text embedding models via DashScopeEmbeddings, as required by Aliyun's official documentation.

Addresses the embedding initialization issue reported in: #8 (comment)

Further testing may be needed by maintainers to verify full compatibility.

[code4DB]

@ZZH-qwq Thanks for your effort. Please attach the snapshot of successful running cases to facilitate the validation :)

[ZZH-qwq]

Certainly. However, the successful implementation currently requires truncating inputs before embedding:

text = [t[:24000] for t in text]
embedding = await embedding_model.aembed_documents(text)

This truncation workaround isn't included in the current PR as it's unrelated to the core fix.

Additionally, note that initializing DashScopeEmbeddings introduces a new dependency on dashscope. Could you please verify whether standard initialization still functions properly without dashscope installed, as long as no Aliyun cloud models are used?

The snapshot: