The switch reports every change as an event (LP-8)

Turning legacy mail protocols off or back on raises
security.legacy-protocols-changed (id 643, info level, also in the packaged
schema), with the scope (policy = server), the new value, who made the
change (accountId), whether listeners closed or reopened (details), which
ones (listenerId), and -- only when a listener could not be put back --
which and why (reason).

It is raised in Server::set_protocol_policy rather than by the JMAP
method, so whatever turns the switch is reported. A /set that changes
nothing -- the switch already where it was asked to be, nothing to close
or reopen -- is not a change and raises nothing.

The event is never an error, but jmap's exhaustive map from security
events to HTTP errors has to name it; it joins the other two that can't
occur there. rustfmt now also wraps LP-6's two over-long lines in
enums_impl.rs, which it flagged along with this change's.

tests/e2e/legacy_protocols.py now gives the server a stdout tracer and
reads events from the container's log: turning the switch off is exactly
one event naming the scope, value, author and listeners closed; setting it
off again raises none; turning it on is one event naming the listeners
reopened. It also proves LP-6's side: seven refused submission sign-ins
are seven auth.legacy-protocol-refused events, and there is no auth.failed
or auth.too-many-attempts among them. All checks pass.

resources/schema/schema.json.sha256

@@ -1 +1 @@
-C32Zc43ANGr52j0cZkTq3IEPrGtbFUX0d2-R91noCho
+7DAGhNQhe_TWHNme6m7dbMaqwfgHWxF31cwHFvqaMHU