feat: expose remote reconnects to client

[Frando]

Fixes #60

Changes:

• Expose a boolean from RemoteConnection::open_bi to indicate whether a new connection was established under the hood or if the previous connection is being reused
• Add a getter for this is_new_connection boolean to Request
• Add the high-level APIs (rpc, server_streaming etc) to Request to make working with the request()-based two-step API easier (step 1: prepare request, which creates the connection if needed and opens the channels. step 2: perform the actual request)
• Adapt the auth example to work well when the server restarts