Address review feedback on Muzi Base support

- rename the board class and files to MuziBaseBoard
- uppercase the build flags (MUZI_BASE, MUZI_BASE_SUPERIO)
- name the superIO envs muzi_base_{duo,uno}_superIO_companion_radio_ble so
  build.sh picks them up
- set MAX_CONTACTS to 350 like the other variants
- move the pin setup from initVariant() into MuziBaseBoard::begin()

variants/muzi_base/target.cpp

@@ -3,7 +3,7 @@
 #include "target.h"
 #include "variant.h"
 
-muzi_baseBoard board;
+MuziBaseBoard board;
 
 RADIO_CLASS radio = new Module(P_LORA_NSS, P_LORA_DIO_1, P_LORA_RESET, P_LORA_BUSY, SPI);