Add OperServ with AKILL network bans

The first operator module. AKILL manages network bans as a typed,
event-sourced list with lazy expiry, mirroring the patterns the other
modules use:

- AKILL ADD [+expiry] <user@host> <reason> stores the ban and drives an
  ircd G-line (applied to matching users already online and to future
  connections); AKILL DEL <mask|number> lifts it; AKILL LIST [pattern]
  shows the live list, numbered. Admin-only.
- Bans are Global events, so every node holds the list and re-asserts each
  one at burst with its remaining duration. Expired bans are hidden lazily
  and dropped at compaction.
- Masks are normalised to user@host (a nick! prefix is stripped, both
  sides lowercased) and an all-wildcard mask is refused.

Email (send_email) is already reachable from the api via ServiceCtx, and
adds AddLine/DelLine to the action vocabulary for any future X-line kinds.

src/main.rs

@@ -20,6 +20,7 @@ use fedserv_chanserv::ChanServ;
 use fedserv_memoserv::MemoServ;
 use fedserv_statserv::StatServ;
 use fedserv_hostserv::HostServ;
+use fedserv_operserv::OperServ;
 use fedserv_example::ExampleServ;
 use fedserv_inspircd::InspIrcd;
 use fedserv_nickserv::NickServ;
@@ -83,6 +84,11 @@ async fn main() -> Result<()> {
             uid: format!("{}AAAAAG", cfg.server.sid),
         }));
     }
+    if enabled("operserv") {
+        services.push(Box::new(OperServ {
+            uid: format!("{}AAAAAH", cfg.server.sid),
+        }));
+    }
     if enabled("example") {
         services.push(Box::new(ExampleServ {
             uid: format!("{}AAAAAC", cfg.server.sid),