fix: Set initial backoff time to 90 days immediately

As per the MSC:
> This MSC recommends homeservers should wait a minimum of 24 hours
> and should wait no longer than 90 days, balancing the need to respect
> the server's intent to be offline whilst allowing for potential future
> changes in server operation or domain ownership.

And as per nex:
> Technically the MSC said it should be up to 90 days, but they'll never
> make me parse cache-control!

src/service/sending/sender.rs

@@ -149,10 +149,10 @@ impl Service {
 					{
 						debug!("{dest} is now unhealthy & stale due to a connect error: {e:?}");
 						self.services.federation.mark_destination_stale(dest);
-						self.services.federation.hit_unhealthy(dest.clone());
+						self.services.federation.hit_unhealthy(dest.clone(), None);
 					} else if e.status_code() != StatusCode::OK {
 						debug!("{dest} is now unhealthy due to error response: {e:?}");
-						self.services.federation.hit_unhealthy(dest.clone());
+						self.services.federation.hit_unhealthy(dest.clone(), None);
 					}
 				}
 				Self::handle_response_err(dest, statuses, &e);