Bug: Individual device volume scaling for AirPods doesn't maintain current volume settings

[ptdarkness]

Describe the bug
Increasing the scalar for AirPods will change the current volume by a corresponding factor. For example, changing the maximum volume from 100% to 200% will double the current volume, and if you were to change from 100% to 50%, the current volume would be halved. This bug was introduced when per device volume scaling was added. Prior to that, scale changes were applied correctly for all devices.

Steps to Reproduce

1. Click the 'Gear' icon in the volume settings
2. Change the volume scaling for an AirPods device
3. Note that the effective volume change by a corresponding factor

Expected behaviour
Volume scaling should not apply any adjustment to the current volume level.

Setup information:

• Audio device used for playback: AirPods
• Audio transmission interface: Bluetooth
• macOS Version: 14.3
• eqMac Version: v1.8.5
• eqMac UI Version: v5.0.7 (local)

Screenshots or Console.app logs
In these screenshots, I increased the maximum scaled volume from 100% to 200%. Instead of maintaining the current volume, it was immediately doubled, and if I had been listening to something, my ears would be hurting.

Additional information
Scalar settings are reset when a device change occurs (see bug ticket #904)