Fix sequence of state setters between cancelling one query and starting another

Summary: Removing one piece of spaghetti reveals another...

Test Plan:
Try this streaming query. It should get results and still be cancellable.
```
import px
df = px.DataFrame(table='http_events', start_time='-2s')
df.pod = df.ctx['pod']
df = df.drop(['time_', 'upid', 'trace_role', 'http_minor_version', 'http_content_type', 'http_resp_message'])
px.display(df.stream())
```

Reviewers: nserrino, michelle, #engineering, philkuz, vihang

Reviewed By: #engineering, vihang

Differential Revision: https://phab.corp.pixielabs.ai/D6709

GitOrigin-RevId: c6df9dfa5289d1a5ef159f1150e95d06856ecf9b

src/ui/src/context/script-context.tsx

@@ -288,8 +288,12 @@ const ScriptContextProvider = (props) => {
 
     const mutation = ContainsMutation(execArgs.pxl);
     const isStreaming = IsStreaming(execArgs.pxl);
-    setLoading(true);
-    setStreaming(isStreaming);
+    // The cancellation above sets a timeout to mark these both as false, to get around a context update timing issue.
+    // In so doing, it pushes that issue downstream, to here, so do the same trick to fix it.
+    setTimeout(() => {
+      setLoading(true);
+      setStreaming(isStreaming);
+    });
 
     if (!execArgs.skipURLUpdate) {
       commitURL(execArgs.liveViewPage, execArgs.id, execArgs.args);