This adds the ability for `TunnelAuth` to also authorize incoming wireguard node IPs, preventing agents from reporting anything other than their static IP generated from the agent ID.
I noticed in testing that the CLI wasn't correctly sending the disconnect message when it shuts down, and thus agents are seeing this as a "lost" peer, rather than a "disconnected" one.
What was happening is that we just used a single context for everything from the netconn to the RPCs, and when the context was canceled we failed to send the disconnect message due to canceled context.
So, this PR splits things into two contexts, with a graceful one set to last up to 1 second longer than the main one.
