Consider moving the extension methods on AblySdkRealtime* contained in DefaultAbly.kt

[lawrence-forooghian]

From @KacperKluka in #868 (comment):

The point of using extension functions is to extend the functionality of objects you can't control. However, right now we have control over the AblySDKRealtime interface so instead of using an extension function we can simply add the closeSuspending() method to the interface 🤔 But this is not critical, so feel free to do it as a part of this PR or create an issue for changing it later 😉

My reply:

I think that if we're going to move those to non-private functions then we need to add tests for them. Currently, their functionality will be tested as part of the tests proposed for DefaultAbly in #869. But if we move this functionality out of the DefaultAbly class this will no longer be the case.

[sync-by-unito]

➤ Automation for Jira commented:

The link to the corresponding Jira issue is https://ably.atlassian.net/browse/SDK-3204