Y333 201224/appflags hex

[yogh333]

No description provided.

[yogh333]

To be merged when LedgerHQ/ledger-device-rust-sdk#227 will me merged and new builder deployed

[fbeutin-ledger]

I know I am a verbose developer, but I really think this code will look way less in a few months and adding a lot of comments as to what we do and why we do it will help us in the long term
Also this swap implementation will be used as reference for other rust swap implementations (including me for boilerplate) so I think we should add much more context comments

[yogh333]

@bboilot-ledger @fbeutin-ledger I did some modifications after your comments.
Regarding the fees, they are supposed to be constant for a Transfer action (see https://docs.near.org/concepts/protocol/gas#cost-for-common-actions). So I always return "0.450 Tgas" as fees. Conversion to a $NEAR value is only possible by retrieving the current gas price, as explained here, so it is not possible to display the fees in $NEAR except by taking the floor price (1 Tgas = 0.0001 $NEAR), which thus can be under-estimated.

[bboilot-ledger]

On my end it looks good, but let's wait for @fbeutin-ledger feedback since he had many comments.