Kernel/SDK: Multiple changes in the rust sdk

What

Multiple modification on the sdk in this MR:

• Renaming Mutez in Narith
• In Narith, use BigUint instead of BigInt with the Sign of the BigInt forced to Plus
• Dynamic encding was used instead of ShortDynamic
• Can now derive NomReader BinWriter or HasEncoding on an enum that contains a type recognize by the encoding-derive crate

Why

For Tezlink, we need to represent N.t types that are corresponding to the Mutez type in the sdk, but it's not to only represent Mutez values (there's gas_limit, storage limit, counter in an operation ...). So we're renaming Mutez to Narith.

Along with some fixes in the rust sdk, short dynamic encoding was not used at a certain place. And also a problem when deriving NomReader on an enum. (the last commit has a little comment about that)

How

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR