Argument grouping for ZK proofs

[fjarri]

Stacked on top of #166

Group secret and public inputs into structs to make it more transparent which variables are substituted at the points of their use (since the variable names in the protocols don't always correspond to the variable names in the proofs)

[codecov]

Codecov Report

Attention: Patch coverage is 89.23077% with 56 lines in your changes missing coverage. Please review.

Project coverage is 93.06%. Comparing base (a7dc794) to head (a2fe42a).

Files with missing lines	Patch %	Lines
synedrion/src/cggmp21/interactive_signing.rs	75.22%	56 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #169      +/-   ##
==========================================
- Coverage   93.23%   93.06%   -0.17%     
==========================================
  Files          36       36              
  Lines        6858     7012     +154     
==========================================
+ Hits         6394     6526     +132     
- Misses        464      486      +22     

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[dvdplm]

lgtm