OptionalchannelchannelHeartbeatInterval overrides the heartbeat interval (ms) for
this attachment. If unset, the client-level default
(ClientOptions.channelHeartbeatInterval, default 5000 ms) applies
to both Realtime and Polling modes.
OptionalsyncsyncMode selects how the channel keeps presence in sync with the server.
Default is SyncMode.Realtime.
SyncMode.Realtime: open a watch stream and run the heartbeat. Required
to receive broadcast events.SyncMode.Polling: heartbeat-only. No watch stream is opened. The
heartbeat refreshes TTL and brings the latest sessionCount. Recommended
for large channels where broadcast is not needed.SyncMode.Manual: no automatic activity. Caller must invoke sync().
AttachChannelOptionsare user-settable options used when attaching channels.