Toolbox window disappears: uncaught `IllegalStateException: RpcClient was cancelled` from environments view after a network change

## Summary

When the Coder plugin's environments view queries `SettingsService.getEnvironmentInfo` over RPC and the underlying RPC channel has been cancelled (which happens on a network drop / network change), the call throws `java.lang.IllegalStateException: RpcClient was cancelled`.
This exception is not caught by the plugin and propagates up to Toolbox's `ComposeWindowsService` as an "Unhandled exception in a window 'Toolbox'".
When this happens, every time you open the toolbox and the plugin again it crashes. Only a toolbox force quit and restart fixes it.

## Environment

- **Coder Toolbox plugin:** v0.9.0 (latest release)
- **JetBrains Toolbox:** 3.5.0.84344
- **OS:** Windows 11 Pro (build 26200)
- **Coder deployment:** self-hosted

## Steps to reproduce

1. Connect to one or more Coder workspaces from the Toolbox Coder plugin (so RPC/SSH channels are live).
2. Trigger a network change/drop. The RPC keepalive then times out / the socket closes, logged as `SocketException: Socket closed` and `KeepaliveTimeoutException: Connection timed out`.
3. Open / return to the Coder plugin's environments view while a previously-connected workspace's RPC channel is in the cancelled state.
4. Now the Toolbox window can no longer be accessed

## Primary stack trace

```
ComposeWindowsService Unhandled exception in a window 'Toolbox':
java.lang.IllegalStateException: RpcClient was cancelled
at kotlinx.rpc.krpc.client.KrpcClient$callServerStreaming$1.invokeSuspend(KrpcClient.kt:265)
at kotlinx.coroutines.flow.SafeFlow.collectSafely(Builders.kt:57)
at kotlinx.coroutines.flow.AbstractFlow.collect(Flow.kt:226)
at kotlinx.coroutines.flow.FlowKt__ReduceKt.first(Reduce.kt:196)
at kotlinx.rpc.krpc.client.KrpcClient.call(KrpcClient.kt:258)
at com.jetbrains.toolbox.agentNetworkApi.settings.SettingsService$$rpcServiceStub.getEnvironmentInfo(SettingsService.kt)
at com.jetbrains.toolbox.viewmodel.DevEnvironmentProviderViewModelImpl$combinedEnvironmentState$$inlined$flatMapLatest$1.invokeSuspend(Merge.kt:190)
... (kotlinx.coroutines flow/combine machinery)
```

## Secondary, related render-thread exception (less frequent)

```
ComposeWindowsService Unhandled exception in a window 'Toolbox':
java.awt.IllegalComponentStateException: component must be showing on the screen to determine its location
at java.desktop/java.awt.Component.getLocationOnScreen_NoTreeLock(...)
at androidx.compose.ui.platform.PlatformWindowContext.convertLocalToScreenPosition-R5De75A(PlatformWindowContext.desktop.kt:132)
at androidx.compose.ui.scene.ComposeSceneMediator$DesktopPlatformContext.convertLocalToScreenPosition-MK-Hz9U(ComposeSceneMediator.desktop.kt:795)
at androidx.compose.ui.node.RootNodeOwner.updatePositionCacheAndDispatch(RootNodeOwner.skiko.kt:229)
```

## Connection
It seems that in general, reconnecting after network change seems to not work sometimes.
The coder workspaces are connected through the coder proxy, no direct connections