Support for non-UTF8 message signature

[hardsetting]

Description

Added support for non-UTF8 messages (aka raw messages).

Changes and tests are in separate commits for ease of review.

Building on top of LedgerHQ#13
Thanks @vldmkr for the amazing rundown provided here.

• Anything that is not a transaction or a UTF8 encoded sequence of bytes is considered a raw message.
• The raw message is displayed in hex format.
• Due to memory constraints we can only show up to 60 hex characters. Anything longer than that will be considered blind signing.
• Made sure the nano app builds fine for all devices, and added test cases for the new feature

Bonus fix:

• It should now be possible to sign messages shorter than 33 bytes

Next steps:

In the future, we can do some work to enable displaying longer messages.
One simple option would be, if the signing message is very long, we can compute the signature ahead of time, so that the memory used to store the signing message can be freed and use for formatting.

[alnoki]

@hardsetting thank you for implementing this feature! This will be crucial for enabling key rotation per aptos-labs/aptos-core#11151

[vldmkr]

@hardsetting Thank you! Everything looks great to me. Great addition to the current release!