Device: Fix call controls setting not applying on AirPods

[d4rken]

What changed

Toggling the "Call Controls" option in device settings (single press = end call vs. mute mic) had no effect on AirPods. Changing the option now takes effect immediately and persists across reconnects.

Technical Context

• Root cause: the setting write was encoded with subtype 0x21 (LibrePods/MagicPodsCore "standard" format), but no real device has ever been captured emitting that subtype — Pro Gen 1, Pro 2 USB-C, and Pro 3 all use the compact format (0x20/0x00). Firmware silently dropped the unknown frame and re-emitted the unchanged state, matching the bug-report log exactly.
• Switched the encoder to compact 0x20 with the single-byte combined mapping that mirrors the existing decoder's compact branch. Verified on Pro 3: echoes now reflect the new value within ~50 ms.
• Same pattern as the rename fix in this file (opcode 0x1A replacing LibrePods' 0x1E, which was also silently ignored).
• Kept the 0x21 decode branch as a forward-compat safety net, but the comment now warns against using it on writes.
• Added init { require(...) } to SetEndCallMuteMic so invalid combinations fail at construction, before the optimistic UI update in AapConnection.send() runs.
• Write path is untested on Pro 2 (Lightning) and AirPods 4 ANC (no session captures); read-side captures for those models are consistent with compact format, so risk is low.