Common protocol key type for serialization of Stm types

[Alenar]

Content

This PR defines a new type in the common: ProtocolKey. This allow to replace previously hex encoded stm types to use the wrapped concrete types without changes to the (de)serialization of the parent types.

The implementation of the two fist types that we worked on, ProtocolSignerVerificationKey & ProtocolSingleSignature, is replaced with a simple type alias.

Pre-submit checklist

• Branch
  • Tests are provided (if possible)
  • Crates versions are updated (if relevant)
  • Commit sequence broadly makes sense
  • Key commits have useful messages
• PR
  • No clippy warnings in the CI
  • Self-reviewed the diff
  • Useful pull request description
  • Reviewer requested
• Documentation
  • Update README file (if relevant)
  • Update documentation website (if relevant)
  • Add dev blog post (if relevant)

Limitation

We can't implement toProtocolKey From/To String (and &str) alongside the already defined From/To T where T is (de)serilizable by serde. This is because String and &str are (de)serilizable by serde so the compiler can't decide which implementation to use if we define both.

To circumvent that we implemented one 'genericly' (the conversion to from strings) and the other conversion is implemented manually for each types, the later operation is made trivial by defining a dedicated macro.

Issue(s)

Relates to #668

[github-actions]

Test Results

    3 files    16 suites   6m 0s ⏱️
639 tests 639 ✔️ 0 💤 0 ❌
677 runs  677 ✔️ 0 💤 0 ❌

Results for commit d465e56.

♻️ This comment has been updated with latest results.

[jpraynaud]

LGTM 👍