fix: set keepalive, improve listen loops

[Frando]

A couple of fixes for things I noticed recently:

• Set a keepalive interval on the client transport config when using the quinn transport with the helpers from the util method. Without this, a connection times out if no rpc calls are issued for 30s (default idle timeout)
• Improve the listen helper functions for both irpc and irpc_iroh:
  • Add remote address to log lines
  • Log errors from handle_connection
  • Poll the JoinSet for finished tasks, otherwise the result list in the join set grows unbounded over time
• Fix the tracing_subscriber setup call in the examples

[rklaehn]

Thanks. The listen loops were in need of some love. I think I mentioned it in some issue somewhere, but can't find it.