Add marshalling for deal

[thehoul]

Folllow up to #609. This PR adds methods to marshal and unmarshal Deal in Pedersen and Rabin VSS compatible with V3 to ensure backward compatibility.

[github-actions]

🔒 Could not start CI tests due to missing safe PR label. Please contact a DEDIS maintainer.

[thehoul]

We discussed on Monday putting the marshaling in the internal code to prevent misuse but it's not possible because it causes a circular import (VSS will need to import internal to have the marshaling methods and internal need the structs from VSS to write the marshaling methods).
So for now, they are in the respective packages (i.e. vss.pedersen and vss.rabin) which I don't think is a bad thing: marhsaling is needed for the logic of the algorithm, not just for compatibility with V3.

Note that to marshal the Deal struct, we also need to marshal a share.PriShare struct which I was able to put in internal without causing a circular import.

[github-actions]

🔒 Could not start CI tests due to missing safe PR label. Please contact a DEDIS maintainer.

[AnomalRoil]

a few changes

[jbsv]

Minor stuff, thanks a lot for all that.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
67.1% Coverage on New Code
2.3% Duplication on New Code

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