Device: Send extended init packet to all AirPods models

[d4rken]

What changed

The extended init packet (0x4D) is now sent to all connected AirPods during the AAP handshake, instead of only to specific newer models. Older devices silently ignore the packet, so this is safe. New H2+ models will automatically get full feature support (Adaptive Transparency, Conversational Awareness during playback) without needing a per-model flag.

Technical Context

• The needsInitExt boolean in PodModel.Features gated whether the 0x4D packet was sent during connection setup. Only 5 H2-chip models had it set to true.
• Research into the librepods project confirmed that they send this packet unconditionally to all devices — older models simply ignore unknown command bytes.
• The risk was asymmetric: missing the packet on a device that needs it causes silent feature degradation (no Adaptive Transparency, Conversational Awareness only works without audio). Sending it to a device that doesn't need it is a no-op.
• Removed needsInitExt from Features entirely and changed encodeInitExt() from nullable to non-null.