MU90 0.7/MK90 FULL BUILD ENVIRONMENT

Build:
  python3 build_rom.py

Test:
  python3 -m unittest discover -s . -p 'test_*.py'

Generated 27C256 ROM:
  dist/mk90_unix_v0.7_27c256.bin

MU90-named identical copy:
  dist/mu90_v0.7_mk90_27c256.bin

Expected SHA-256:
  e217109ed2c2ce022e94322ee3debef5d124324a285ab56f99566fc943fd3728
