On dual-nozzle printers (H2C, H2D Pro) with multiple AMS units, usage
tracking attributed filament consumption to the wrong spools. The MQTT
mapping field — a snow-encoded array mapping slicer slots to physical
AMS trays — was preserved in state but never parsed.
Add _decode_mqtt_mapping() to convert snow encoding (ams_hw_id * 256 +
slot) to bambuddy global tray IDs. Insert as priority 2 in the mapping
resolution chain, after print_cmd ams_mapping but before queue/tray_now
fallbacks. Works for all printer models and print sources.