RealtimeChannel: Handle `DETACHED` while not requesting detach

[owenpearson]

spec: RTL13

• If ATTACHED or SUSPENDED, reattempt attach (RTL13a)
• If RTL13a fails, or the channel is already ATTACHING, the channel should move to SUSPENDED and retry indefinitely after channel_retry_timeout (RTL13b)
• Retries defined by RTL13b should be cancelled if the client is no longer CONNECTED (RTL13c)

[sync-by-unito]

➤ Automation for Jira commented:

The link to the corresponding Jira issue is https://ably.atlassian.net/browse/SDK-3300