Upgrade to protocol v5: message update/delete/append, PublishResult, Stats rewrite

[matt423]

Summary

Upgrades the SDK from protocol version 2 to 5, adding message lifecycle operations and bringing the Stats model in line with the current Ably specification.

• Update, delete, append messages on REST (channel.update_message, channel.delete_message, channel.append_message) and Realtime channels (RSL15, RTL32)
• PublishResult returned from publish with message serials (RSL1n, PBR2a)
• UpdateDeleteResult returned from update/delete/append with version serial (UDR2a)
• MessageOperation model for operation metadata on update/delete/append (MOP)
• Complete Message::ACTION enum with all TM5 values (message_create, message_update, message_delete, meta, message_summary, message_append)
• Stats model rewritten to match spec v2.1+ (TS12): flat entries hash replaces nested accessors; all Stats sub-types removed (TS4–TS9 deleted from spec)

Breaking changes

• Rest::Channel#publish returns PublishResult instead of Boolean
• Realtime::Channel#publish deferrable yields PublishResult instead of Message/Array<Message>
• Stats nested accessors (all, inbound, outbound, persisted, connections, channels, api_requests, token_requests) replaced by flat entries hash (TS12r) — use stat.entries['messages.all.all.count'] instead of stat.all.all.count
• Stats::MessageTraffic, Stats::MessageTypes, Stats::MessageCount, Stats::ConnectionTypes, Stats::RequestCount, Stats::ResourceCount removed
• Stats#interval_granularity replaced by Stats#unit (TS12c)

New models

Model	Spec	Purpose
PublishResult	RSL1n, PBR2a	Wraps publish response with serials array
UpdateDeleteResult	UDR2a	Wraps update/delete/append response with version_serial
MessageOperation	MOP	Operation metadata (client_id, description, metadata)

REST examples

client = Ably::Rest::Client.new(key: 'key')
channel = client.channels.get('chat')

# Publish — now returns PublishResult with serials
result = channel.publish('greeting', 'Hello!')
serial = result.serials.first  #=> "01826232781:0"

# Batch publish
result = channel.publish([
  { name: 'chat', data: 'Hello' },
  { name: 'chat', data: 'World' }
])
result.serials  #=> ["01826232781:0", "01826232781:1"]

# Update
channel.update_message({ serial: serial, data: 'Edited' })

# Delete
channel.delete_message({ serial: serial })

# Append
channel.append_message({ serial: serial, data: { reaction: 'heart' } })

# With operation metadata
channel.update_message(
  { serial: serial, data: 'Fixed' },
  { description: 'Typo fix', metadata: { 'reason' => 'spelling' } }
)

Realtime examples

EventMachine.run do
  client = Ably::Realtime::Client.new(key: 'key')
  channel = client.channels.get('chat')

  channel.attach do
    channel.publish('greeting', 'Hello!') do |result|
      serial = result.serials.first

      channel.update_message({ serial: serial, data: 'Edited' }) do |update_result|
        puts update_result.version_serial
        client.connection.close { EventMachine.stop }
      end
    end
  end
end

Test plan

• All 1261 unit tests pass
• All 2516 acceptance tests pass (0 failures, 5 pending)
• SPEC.md regenerated with zero failure markers

[lmars]

@matt423 I'm going to review this, but just based on the description:

Breaking changes

I don't think we can make this change in a patch release if it includes breaking changes, were you intending this to be a major version bump? If not, then I think we need to do it in a backwards compatible way similar to how we're doing it for Go in ably/ably-go#697 (i.e. by adding a new PublishWithResult method which returns PublishResult whilst leaving Publish the same, and keeping stats the same by sticking with protocol v2 for stats).