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/imex.rs

@@ -90,7 +90,7 @@ pub async fn imex(
     let cancel = context.alloc_ongoing().await?;
 
     let res = {
-        let _guard = context.scheduler.pause(context.clone()).await?;
+        let _guard = context.scheduler.pause(context).await?;
         imex_inner(context, what, path, passphrase)
             .race(async {
                 cancel.recv().await.ok();