feat(RAG): 更新RAG模块代码和文档

refactor: 简化Embeddings和LLM类实现，移除不必要依赖
docs: 更新文档内容，添加硅基流动API使用说明
chore: 更新requirements.txt依赖版本

docs/chapter7/RAG/requirements.txt

@@ -1,14 +1,28 @@
-openai
-zhipuai
-numpy
-python-dotenv
-torch
-torchvision
-torchaudio
-transformers
-tqdm
-PyPDF2
-markdown
-html2text
-tiktoken
-beautifulsoup4
+annotated-types==0.7.0
+anyio==4.9.0
+beautifulsoup4==4.13.4
+bs4==0.0.2
+certifi==2025.6.15
+charset-normalizer==3.4.2
+distro==1.9.0
+h11==0.16.0
+httpcore==1.0.9
+httpx==0.28.1
+idna==3.10
+jiter==0.10.0
+markdown==3.8.2
+numpy==2.3.0
+openai==1.88.0
+pydantic==2.11.7
+pydantic-core==2.33.2
+pypdf2==3.0.1
+python-dotenv==1.1.0
+regex==2024.11.6
+requests==2.32.4
+sniffio==1.3.1
+soupsieve==2.7
+tiktoken==0.9.0
+tqdm==4.67.1
+typing-extensions==4.14.0
+typing-inspection==0.4.1
+urllib3==2.5.0