chanserv: SET TOPICLOCK and KEEPTOPIC (topic subsystem)

Adds topic tracking: a TopicChange event (parsed from InspIRCd FTOPIC, our own
changes filtered by SID like FMODE) and a stored topic on the channel, folded
through the event log. TOPICLOCK reverts a topic change by a user without
op-level access back to the stored topic; KEEPTOPIC remembers the topic and
restores it when a registered channel is recreated. Both via the typed
ChanSettings path; shown in INFO. Parse + engine tests cover both.

chanserv/src/lib.rs

@@ -106,6 +106,8 @@ impl Service for ChanServ {
                         if info.private { opts.push("PRIVATE"); }
                         if info.peace { opts.push("PEACE"); }
                         if info.secureops { opts.push("SECUREOPS"); }
+                        if info.keeptopic { opts.push("KEEPTOPIC"); }
+                        if info.topiclock { opts.push("TOPICLOCK"); }
                         if !opts.is_empty() {
                             ctx.notice(me, from.uid, format!("  Options    : {}", opts.join(", ")));
                         }