mrp: report a HomePod stereo pair leader as powered on

[teriu]

Fixes #2916

Problem

A HomePod mini that leads a stereo pair reports PowerState.Off while it is playing over AirPlay. Its DEVICE_INFO_MESSAGE carries logicalDeviceCount: 0, and MrpPower._get_power_state maps 0 to Off. Playback state and metadata do arrive correctly. In Home Assistant's apple_tv integration, though, an Off player is shown as off, and all of its media attributes are dropped, so a playing pair looks switched off.

The leader's DEVICE_INFO while playing (IDs redacted):

name: "L HomePod"
modelID: "AudioAccessory5,1"
systemBuildVersion: "24J361"
logicalDeviceCount: 0
groupName: "Main Bedroom"
isGroupLeader: false
isAirplayActive: true
clusterID: "<redacted>"
clusterLeaderID: "<this device's own deviceUID>"
clusterType: 1
isClusterAware: true

Change

When logicalDeviceCount is 0, _get_power_state now also checks the cluster fields. A cluster-aware device whose clusterLeaderID equals its own deviceUID is reported as On. The pair's other member, and an Apple TV that is asleep (which sends no cluster fields), still report Off, so the existing behaviour for Apple TVs is unchanged.

Testing

• New parametrised unit test, test_power_state_from_device_info, covers: count 1 → On, count 0 → Off, pair leader → On, pair follower → Off, and a sleeping Apple TV with no cluster fields → Off. The leader case fails without this change.
• Full suite: 1251 passed, 6 skipped. Run on Python 3.13; 3.14 wasn't available on the machine I used.
• black and isort are clean. flake8, mypy and pylint report the same as on master.
• Against real hardware with atvremote --scan-hosts <leader> power_state playing, on a HomePod mini stereo pair running software 27.0 (24J361):

	power_state	playing
leader, master	PowerState.Off	Playing, full metadata
leader, this branch	PowerState.On	Playing, full metadata
follower, this branch	PowerState.Off	Playing

Open question

The follower also reports Device state: Playing with metadata. I left it as Off, to keep the change narrow and because clients control a pair through its leader. Happy to treat any cluster member as On instead, if you'd prefer that.

🤖 Generated with Claude Code