memoserv: complete + improve the memo service

Finish MemoServ on the typed, event-logged memo model: Db memo_send/list/read/
del/unread_memos + Store facade, and a new fedserv-memoserv crate (a default
service). Beyond the basics: SEND caps a mailbox (30) so nobody's flooded, READ
takes <num>|NEW|ALL, DEL takes <num>|ALL, LIST previews and flags unread, and
NickServ notifies you of waiting memos on login. Memos persist and federate
(Global scope) like other account data. Also lands NetAction::QuitUser (BotServ
plumbing). Data + delivery/login-notify tests.

inspircd/src/lib.rs

@@ -261,6 +261,7 @@ impl Protocol for InspIrcd {
             }
             // SVSNICK <uid> <newnick> <nickts> — the new nick takes the current
             // time as its TS so it wins any collision resolution.
+            NetAction::QuitUser { uid, reason } => vec![format!(":{} QUIT :{}", uid, reason)],
             NetAction::ForceNick { uid, nick } => {
                 let now = SystemTime::now().duration_since(UNIX_EPOCH).map(|d| d.as_secs()).unwrap_or(self.ts);
                 vec![self.from_us(format!("SVSNICK {} {} {}", uid, nick, now))]