Add REST 'Batch Operations' features, including for `publish` (`BO2a`) and `getPresence` (`BO2b`)

[QuintinWillison]

As pointed out by @lmars in #3 (comment).

At the time of writing, this has not been implemented in any SDKs, despite having been added to the features spec in ably/docs#1421 and enhanced in ably/docs#1477 (RSC22).

There is an old implementation in ably-java, which does not align with the features spec.. See publishBatch methods and publishBatchAsync methods which were added in ably/ably-java#439.

See:

• Improvements to batch operations specification#9 which might have implications
• Implement batch operations feature ably-js#989
• Implement batch operations feature ably-ruby#364
• Implement batch operations feature ably-java#790
• Implement batch operations feature ably-cocoa#1421
• Implement batch operations feature ably-dotnet#1151
• Implement batch operations feature ably-python#273
• Implement batch operations feature ably-go#529
• Implement batch operations feature ably-php#158
• Implement batch operations feature ably-rust#10

[sync-by-unito]

➤ Automation for Jira commented:

The link to the corresponding Jira issue is https://ably.atlassian.net/browse/SDK-2727

[SimonWoolf]

NB: realtime now implements the response requested by Owen as part of his proposed changes at ably/specification#9 , when the sdk specifies protocol version 2.0. (Which means it would not make sense for any new sdk to work on batch support against protocol v1, as they'd need to change it again once the lib updates to v2; so any work should happen against the relevant protocol-v2 integration branch)