Read the pad, detect unknown ones, layout editor

added a feature that now can read the inputs off the board, meaning if you already have saved settings and you uninstall / reinstall the app or use it on a new device it can auto detect what each key has saved.

using the above feature i now also do believe it is possible to auto detect the macros pads rough layout / how many keys and dials it has!. hopfully this means that more people can use the app easily without needing to hard code a bunch of new layouts. its not truly universal but it should open the door to much more pads working out of the box right now!

and lastly in case the extra layouts do work i made a little layout editor so you can the app to look like your actual macropad!

macropad.py

@@ -223,6 +223,47 @@ def native_media(report_id, action, usage, layer=1):
     return [bytes([report_id]) + bytes(data), native_commit(report_id)]
 
 
+# ----------------------------------------------------------- reading back
+#
+# The pad can be read, which we only found by capturing the vendor software's
+# "view settings" button. Two commands, both answered on the interrupt IN
+# endpoint of the same report id:
+#
+#   0xFB  what are you?    reply: 03 fb <keys> <knobs>
+#   0xFA  send me a layer  reply: one report per control, magic 0xFA, then
+#                                 nothing more
+#
+# Observed, reading layer 1:
+#   03 fa 0f 03 01 02 ...          request (trailing bytes were uninitialised
+#                                  memory in the vendor program; zeros work)
+#   03 fa 02 01 01 00 ... 01 05 17 key2 is ctrl+alt+t
+#   03 fa 10 01 02 00 ... 01 ea 00 dial 1 left is volume down
+
+MAGIC_INFO = 0xFB
+MAGIC_READ = 0xFA
+KEY_SLOTS = 0x0F      # the firmware keeps 15 key slots whatever the pad has
+KNOB_SLOTS = 3
+LAYERS = 3
+
+
+def native_info(report_id):
+    """Ask the pad what it is. Reply carries the key and knob counts."""
+    data = bytearray(REPORT_LEN - 1)
+    data[0] = MAGIC_INFO
+    return bytes([report_id]) + bytes(data)
+
+
+def native_read(report_id, layer=1):
+    """Ask the pad for every control in one layer."""
+    data = bytearray(REPORT_LEN - 1)
+    data[0] = MAGIC_READ
+    data[1] = KEY_SLOTS
+    data[2] = LAYERS
+    data[3] = layer
+    data[4] = 2
+    return bytes([report_id]) + bytes(data)
+
+
 # ------------------------------------------------------- legacy protocol
 #
 # The older format. Unlike Extended, a single binding is a *sequence* of