Added the CDJ-900NXS firmware patcher.

Takes the official C900NXS.UPD (1.31, checked by SHA-256), lets you choose
mods in a list (arrows, space, enter; numbers where the terminal cannot pass
keys), patches the application with the emulator checkout's
mods/patch_cdj900nxs.py, packs it and writes a new C900NXS.UPD labelled 1.32.

Only the application is replaced: the boot loader and recovery records,
MAIN's S0/S7 records, DRIV and PANL are copied byte for byte and checked again
on the finished file, which is also unpacked the boot loader's way and
compared with the patched application. --stock differs from the official file
in the version label and its CRC only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,4 @@
+out/
+*.UPD
+__pycache__/
+.pytest_cache/