fix(nut17): decode notification payloads with subscription kind

NUT-17 notification payloads are ambiguous without the subscription
kind. Quote response shapes overlap and tolerate unknown fields, so
shape-based decoding can select the wrong payload variant.

Add a kind-aware payload decoder and use it in the wallet subscription
client while preserving the existing generic payload deserialization
surface for backports.

This prevents onchain and custom quote notifications from being decoded
as the wrong payload variant.

Author: thesimplekid