fix: multi relay connectivity (#8550)

this PR, created together with @adbenitez, improves the connectivity
state passed to UI, which has changed a lot since multi relay:

- change the algorithm for `get_connectivity()`: this is roughly the
"best" connectivity of all relays now, so if one is connected, we're
already fine. this was discussed widely one to one, and that part
already closes #8554

- the PR adds a test for that, previously, that was untested

- additionally, do not regard unpublished relays in
`get_connectivity()`: e.g. unpublished relays are no longer given to
peers - so if only that is connected, the overall state should not be
"connected". therefore, we just ignore unpublished relays there

- in `get_connectivity_html()`, we continue showing unpublished relays,
however, we tune them down visually and flag them as such

- for the docs, remove the "range for some future use" wording. it was
never used like that, and that future will probably not arrive :)

<img width="320"
src="https://github.com/user-attachments/assets/1805c525-72d1-4197-b865-6e2d6fbc8819"
/>

---------

Co-authored-by: Hocuri <hocuri@gmx.de>

src/scheduler.rs

@@ -321,6 +321,9 @@ struct SchedBox {
 
     /// IMAP loop task handle.
     handle: task::JoinHandle<()>,
+
+    /// Relay published status.
+    is_published: bool,
 }
 
 /// Job and connection scheduler.
@@ -637,7 +640,9 @@ impl Scheduler {
         let mut inboxes = Vec::new();
         let mut start_recvs = Vec::new();
 
-        for (transport_id, configured_login_param) in ConfiguredLoginParam::load_all(ctx).await? {
+        for (transport_id, configured_login_param, is_published) in
+            ConfiguredLoginParam::load_all(ctx).await?
+        {
             let (conn_state, inbox_handlers) =
                 ImapConnectionState::new(ctx, transport_id, configured_login_param.clone()).await?;
             let (inbox_start_send, inbox_start_recv) = oneshot::channel();
@@ -654,6 +659,7 @@ impl Scheduler {
                 folder,
                 conn_state,
                 handle,
+                is_published,
             };
             inboxes.push(inbox);
             start_recvs.push(inbox_start_recv);