botserv: ASSIGN / UNASSIGN a bot to a channel

A channel gains a typed assigned_bot (event-logged, snapshotted). ASSIGN
<#channel> <bot> / UNASSIGN <#channel> is founder-gated (or admin oper). The
engine reconcile now also diffs channel assignments against tracked bot
memberships: a live bot IJOINs its assigned channels and PARTs unassigned ones
(new ServiceJoin/ServicePart actions), at burst and after commands; a deleted
bot's memberships are dropped. Engine test for join-on-assign / part-on-unassign.

inspircd/src/lib.rs

@@ -262,6 +262,8 @@ 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::ServiceJoin { uid, channel } => vec![format!(":{} IJOIN {}", uid, channel)],
+            NetAction::ServicePart { uid, channel } => vec![format!(":{} PART {}", uid, channel)],
             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))]