Added support for Soundcore sleep A20 a6611 in the Android app and lib

[akoerner]

Add Soundcore Sleep A20 (A6611) support

Added cursory support for the A20. The features from the official app that I actually use ar find my device and Bluetooth/sleep mode toggle so this is what I implemented. Protocol was snooped via android HCI capture. Testing with two separate hardware revisions running different firmware.

A20 support

• New SoundcoreA6611 model. The state packet is parsed per tools/soundcore-device-faker/devices/a6611.toml and verified against real packets from firmware 01.57 and 03.22.
• Read-only info: TWS status, battery levels, dual firmware version and serial number.
• Sleep Mode toggle: sends 0x01 0xa9 (1 = Bluetooth, 0 = Sleep), and follows the earbuds' 0x01 0x14 notification, so changes from an earbud double tap or the official app are reflected.
• Find Left/Right Earbud toggles: send 0x10 0x89 with body [left, right, 0].
• All command encodings were captured from the official app and match it byte for byte.

Find Device safety

Turning on Find Device requires confirming a hearing-damage warning; Cancel is the default. These settings are excluded from quick presets and widgets.

Shared fixes

• watch_for_changes stopped notifying the UI once change_notify closed, which happens immediately on devices like the A20.
• MultiQueue::cancel deadlocked any request queued behind a timed-out one.