`AblyRealtime` class `close()` implementation should throw `Exception`

[QuintinWillison]

If it's properly conforming to AutoCloseable.

I'm pretty sure this would be a breaking change.

Though I'm actually a bit confused as to why we're even able to compile in this state, but perhaps there's some Java language edge case that I'm unaware of. :confused:

• implements: https://github.com/ably/ably-java/blob/95790cf0a7bc65ba360964a04f01a0c3bf169278/lib/src/main/java/io/ably/lib/realtime/AblyRealtime.java#L24
• implementation overrides: https://github.com/ably/ably-java/blob/95790cf0a7bc65ba360964a04f01a0c3bf169278/lib/src/main/java/io/ably/lib/realtime/AblyRealtime.java#L81

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