refactor: extract device registry and protocol from canvas.py

Move the master device list (206 entries) and category sets
(phidget, nonSerial, nonTemp, special, binary devices) from
canvas.py into a standalone device_registry module.

Define RoasterProtocol and ScaleProtocol in device_protocol.py
to document the implicit interface that 30+ machine drivers
already implement.

All 2252 existing tests pass. Zero behavior change.

Author: danielislas3

src/artisan.pro

@@ -31,6 +31,8 @@ SOURCES = \
     artisanlib/cup_profile.py \
     artisanlib/curves.py \
     artisanlib/designer.py \
+    artisanlib/device_protocol.py \
+    artisanlib/device_registry.py \
     artisanlib/devices.py \
     artisanlib/dialogs.py \
     artisanlib/events.py \