Review connections handling when Load Balancing mode is active

[DanielePalaia]

Describe the bug

Similar to:

#235

When Load Balancer mode is activated the open connections in
https://github.com/rabbitmq/rabbitmq-stream-rust-client/blob/main/src/producer.rs#L144

Are never closed in the .close() method letting connections open.

Same for Consumer

Reproduction steps

1. You can check the example in:
   Implement super_stream  #232

Expected behavior

All connections should be closed when .close connection is invoked.

Additional context

No response