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.

Cargo.lock

@@ -333,6 +333,7 @@ dependencies = [
  "fedserv-inspircd",
  "fedserv-memoserv",
  "fedserv-nickserv",
+ "fedserv-operserv",
  "fedserv-statserv",
  "hmac",
  "pbkdf2",
@@ -406,6 +407,13 @@ dependencies = [
  "fedserv-api",
 ]
 
+[[package]]
+name = "fedserv-operserv"
+version = "0.0.1"
+dependencies = [
+ "fedserv-api",
+]
+
 [[package]]
 name = "fedserv-statserv"
 version = "0.0.1"