epicardium: add USB composite device, implement USB de-init

epicardium/cdcacm.c

epicardium/cdcacm.h

epicardium/descriptors.h

epicardium/epicardium.h

epicardium/main.c

epicardium/modules/filesystem_fat.c

epicardium/modules/meson.build

epicardium/modules/usb.c

...lications/EvKitExamples/USB_CompositeDevice/descriptors.h

...sdk/Applications/EvKitExamples/USB_CompositeDevice/main.c

pycardium/meson.build

pycardium/modules/fat_file.c

pycardium/modules/qstrdefs.h