add --nfc flag to use NFC apdu media

[yrichard-ledger]

No description provided.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 39.71292% with 126 lines in your changes missing coverage. Please review.

Project coverage is 43.86%. Comparing base (9913397) to head (6518a6d).

Files with missing lines	Patch %	Lines
speculos/mcu/transport/usb.py	39.25%	65 Missing ⚠️
speculos/mcu/transport/nfc.py	28.26%	33 Missing ⚠️
speculos/mcu/seproxyhal.py	23.07%	10 Missing ⚠️
speculos/mcu/transport/interface.py	73.07%	7 Missing ⚠️
speculos/main.py	0.00%	5 Missing ⚠️
speculos/mcu/transport/__init__.py	54.54%	5 Missing ⚠️
src/bolos/os.c	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #519   +/-   ##
=======================================
  Coverage   43.85%   43.86%           
=======================================
  Files         122      125    +3     
  Lines       12358    12448   +90     
  Branches      993      993           
=======================================
+ Hits         5420     5460   +40     
- Misses       6603     6653   +50     
  Partials      335      335           

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[lpascal-ledger]

Some comments on my latest changes:

• Added the NFC flag in Speculos OS settings on Flex and Stax. We could add an argument to be able to configure it at runtime, but I don't have clear use case for this and didn't though it was worth it for now.
• As USB and NFC are exclusive (Speculos is started with NFC xor HID xor U2F communication), there is little point instantiating and managing a .usb and a .nfc variable. As they share similar behavior (with only different names), I merged them under the same TransportLayer mother class, and instantiate it from a factory function build_transport.
• HID and U2F classes were managed through composition in USB, which led to callback injection, backward dependencies (HID and U2F inherit from a Transport class, but are instrumented through a USB(TransportLayer) class (which is no transport) and weird interface (the factory function knows the transport - HID, U2F, NFC- but only deals with NFC and "USB", which itself manages HID and U2F).
  Now HID and U2F are (inheritance) USBTransport, which is (inheritance) itself a TransportLayer, just like NFC is also a TransportLayer. All can be easily instantiated into the factory function.
• As --nfc and --usb argument could obstruct each other, and --usb feels deprecated now that NFC is available (and maybe bluetooth someday?), I rather added a --transport argument superseeding the --usb one, which is now flagged as deprecated.