Add IStreamChatClient.SuspendConnectionAsync (non-permanent disconnect)

[harlan]

Adds a high-level way to close the websocket without ending the user session, for callers that know the client is about to stop pumping Update() — typically an app being backgrounded.

Why

Messages are received on a background timer thread but only handled from Unity's main loop. When the main loop stops, the receive queue fills with nothing draining it. A consumer that knows this is about to happen wants to close the socket deliberately and have it come back on resume.

The only high-level disconnect today is DisconnectUserAsync(), which calls DisconnectAsync(permanent: true) → ReconnectScheduler.Stop(). That is one-way: _isStopped is never cleared and the scheduler exposes no restart, so a client disconnected that way never auto-recovers. The non-permanent variant already exists, but only on InternalLowLevelClient, which is internal to the StreamChat.Core asmdef and therefore unreachable from a consumer assembly without an InternalsVisibleTo we did not want to add.

Change

A pass-through to DisconnectAsync(permanent: false), which leaves the reconnect scheduler armed. Because the scheduler schedules against the Unity clock (frozen while the app is paused), the reconnect fires on the first frame after resume and re-hydrates missed events through the usual /sync catch-up.

Purely additive — no existing behavior changes. StreamChatClient is the only implementer of IStreamChatClient in the repo.

This would fold away if the SDK ships its own Suspend()/Unsuspend(), which StreamChatLowLevelClient.DisconnectAsync already contemplates in a TODO — if you'd rather build that instead, we're happy to drop this in favor of it.

Testing

No test added: the behavior is a one-line delegation whose observable effect is the reconnect scheduler's internal state, which the current test setup has no seam for.

[sierpinskid]

Hey Harlan — thanks for your contribution. The diagnosis is right: DisconnectUserAsync is logout, and when Update() is about to stop you need a way to drop the socket without ending the session so the receive queue does not pile up.

We went with a slightly different shape in the upcoming release rather than merging this as-is.

SuspendConnectionAsync leaves reconnect to the scheduler, which is scheduled against Unity time. That works when the OS freezes the clock (classic app pause). It does not work when Update() stops but time keeps moving — a hidden WebGL tab, and some editor cases.

By default, the SDK now pauses the socket when the app goes to the background and resumes it when the app returns to the foreground, so you should not need to wire this yourself. If you want more control, set IStreamClientConfig.DisconnectOnApplicationPause to false and call PauseConnectionAsync() / ResumeConnectionAsync() yourself. Either way, the session is kept; recovery (/sync + re-watch) runs as on any reconnect.

We are closing this PR in favor of #238.