[CHA-RL9] Ensure Room ATTACHED before performing room operations over realtime

[sacOO7]

• Currently, every room operation over realtime needs to check for RoomStatus.ATTACHED state.
• Explicit spec CHA-RL9 added for the same -> chat: add CHA-RL9 to explain "attaching piggyback" ably/specification#232
• Implementation for the same can be extracted as a common method ensureAttached as a part of Room.
• Reference swift PR -> [ECO-5127] Implement CHA-RL9 ably-chat-swift#144

┆Issue is synchronized with this Jira Task by Unito

[sacOO7]

Make RoomStatus and Error variables thread safe as per -> https://github.com/ably-labs/ably-chat-kotlin/pull/61/files#r1856161083