Overhaul stats: Add announced `Peer` to UDP core `announce` event

[josecelano]

Depends on: #1341
Relates to: #1376

IMPORTANT: This has to be implemented after #1341.

I'm refactoring events to include more metadata:

pub enum Event {
    UdpConnect { context: ConnectionContext },
    UdpAnnounce { context: ConnectionContext },
    UdpScrape { context: ConnectionContext },
}

#[derive(Debug, PartialEq, Eq)]
pub struct ConnectionContext {
    client_socket_addr: SocketAddr,
    server_socket_addr: SocketAddr,
}

It would also be convenient to include information about the announce request, in the event, like the peer.

Read this for more information about how to include the announced peer data.

[josecelano]

Closed via #1473