rag_helper performance issues when indexing multiple files

Whenever the `rag_tool` indexes multiple files, it needs to initialize weaviate and the embedding models, which takes far too long. https://github.com/supercog-ai/agentic/blob/f6ad85d13a409117b67196a7b8e1d3021c450ce0/src/agentic/utils/rag_helper.py#L164C9-L172C70 A rag_index_multiple_files should be made, that takes a list of paths.