feat: better error handling for client

[tchardin]

This adds handling for common errors:

• Dial failed. The peer isn't reachable. Recovers so we can dial other peers without restarting the client.
• Content not found. Provider sends a ContentNotFound status. Abort the request and return the error.
• Disconnected. Provider went offline or reset the connection during a transfer. Cleanup and try again.
• Rejected. The request input did not meet the provider validation. Abort the request and return the error.