p2p: Track in-progress inbound node IDs (pre-Peer) to avoid dialing them.

[the-shadow-coder]

Closes #33197

This PR adds a pendingInbound map in server.go to track in-progress inbound connections (after encryption handshake, before becoming a full peer). The server notifies the dial scheduler via new inboundPending() and inboundCompleted() methods, allowing checkDial() to skip nodes that are already connecting to us. This prevents the race condition where we attempt to dial a node while it's simultaneously dialing us, saving network resources and avoiding duplicate connections. Added tests in both dial_test.go and server_test.go to verify the behavior