重构代码，实现相对导入

rag_indexer/__init__.py

@@ -23,9 +23,9 @@ Offline RAG Indexer module.
     >>> await builder.build_from_file("document.pdf")
 """
 
-from rag_indexer.index_builder import IndexBuilder, IndexBuilderConfig, DocstoreConfig
-from rag_indexer.loaders import DocumentLoader
-from rag_indexer.splitters import SplitterType, get_splitter
+from .index_builder import IndexBuilder, IndexBuilderConfig, DocstoreConfig
+from .loaders import DocumentLoader
+from .splitters import SplitterType, get_splitter
 
 # 从 rag_core 重新导出常用组件
 from rag_core import (