Mintlayer Core primitive types

Here we have certain primitive types copied from Mintlayer Core and intended for use in hardware wallets' firmware/apps in no_std mode.

Notes:

• The types in this repository are not always identical to those from Mintlayer Core, however they are encode-compatible with them.
• Ideally, we should get rid of the code duplication and, instead, extract the Mintlayer Core's "foundational" crates ¹ into a separate repository and make them usable (in a limited way) in no_std mode.

Footnotes

1. I.e. common and crypto as well as the utility crates that they depend on - utils, serialization, logging etc. ↩