Three interrelated bugs in AMS info field parsing caused AMS units
to appear on the wrong nozzle on H2D dual-nozzle printers:
1. Info field parsed as decimal instead of hex (BambuStudio uses
std::stoull with base 16)
2. Extruder ID extracted as 1-bit instead of 4-bit field (bits 8-11)
3. Partial MQTT updates replaced the full extruder map instead of
merging into it