fix: get_connectivity(): Get rid of locking SchedulerState::inner (#7124)

`get_connectivity()` is expected to return immediately, not when the scheduler finishes updating its
state in `start_io()/stop_io()/pause_io()`, otherwise it causes app non-responsiveness.

Instead of read-locking `SchedulerState::inner`, store the `ConnectivityStore` collection in
`Context` and fetch it from there in `get_connectivity()`. Update it every time we release a write
lock on `SchedulerState::inner`.

src/config.rs

@@ -734,7 +734,7 @@ impl Context {
         Self::check_config(key, value)?;
 
         let _pause = match key.needs_io_restart() {
-            true => self.scheduler.pause(self.clone()).await?,
+            true => self.scheduler.pause(self).await?,
             _ => Default::default(),
         };
         self.set_config_internal(key, value).await?;