make new agent for each request

[emrgnt-cmplxty]

[!IMPORTANT] Instantiate a new R2RStreamingRAGAgent for each request in retrieval_service.py and remove a newline in streaming_rag_pipe.py.

• Behavior:
  • Instantiate a new R2RStreamingRAGAgent for each request in agent() in retrieval_service.py.
• Misc:
  • Remove unnecessary newline in _run_logic() in streaming_rag_pipe.py.

^{This description was created by for a09dd178cf5f32240e2a27ec2d3ebe62f70f0d71. It will automatically update as commits are pushed.}