Scaffold the federated services daemon

Protocol-agnostic core: a Protocol trait maps raw server-to-server lines to a
normalized event/action model, so the engine never touches a raw line and a new
ircd is one new module. Adds event-log state (state is a fold over the log) and
a service framework. First protocol impl links to an InspIRCd (insp4) uplink —
completes the CAPAB/SERVER handshake, bursts, and introduces NickServ.

src/proto/mod.rs

@@ -0,0 +1,38 @@
+// Protocol abstraction. The engine only ever sees NetEvent / NetAction; raw
+// server-to-server lines live entirely behind a Protocol impl. Adding another
+// ircd later means one new module, engine untouched.
+pub mod inspircd;
+
+// Normalized inbound facts, translated from the uplink's raw lines.
+#[derive(Debug, Clone)]
+pub enum NetEvent {
+    Registered,
+    EndBurst,
+    Ping { token: String, from: Option<String> },
+    Privmsg { from: String, to: String, text: String },
+    Quit { uid: String },
+    Unknown { line: String },
+}
+
+// Normalized outbound intents the engine wants performed on the network.
+#[derive(Debug, Clone)]
+pub enum NetAction {
+    Burst,
+    EndBurst,
+    Pong { token: String, from: Option<String> },
+    IntroduceUser { uid: String, nick: String, ident: String, host: String, gecos: String },
+    Privmsg { from: String, to: String, text: String },
+    Notice { from: String, to: String, text: String },
+    Raw(String),
+}
+
+pub trait Protocol: Send {
+    /// Lines to send immediately on connect (auth / capability negotiation).
+    fn handshake(&mut self) -> Vec<String>;
+    /// One raw inbound line -> zero or more normalized events.
+    fn parse(&mut self, line: &str) -> Vec<NetEvent>;
+    /// One normalized action -> the raw line(s) that realise it.
+    fn serialize(&mut self, action: &NetAction) -> Vec<String>;
+    /// Our own server id, used as the source prefix for server-sourced lines.
+    fn sid(&self) -> &str;
+}