[zk-sdk] Flatten out arguments for ciphertext validity proofs

[samkim-crypto]

Problem

In the ciphertext validity proofs, the argument variables to functions are grouped into tuples that are related to each other. It was done this way to tidy things up in the beginning, but it actually seems to make the syntax a lot more messy.

Summary of Changes

Flatten out the argument variables as was also done in #1084.

Fixes #

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.1%. Comparing base (9403ca6) to head (33676f1).
Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##           master    #1134     +/-   ##
=========================================
- Coverage    82.1%    82.1%   -0.1%     
=========================================
  Files         880      880             
  Lines      235665   235633     -32     
=========================================
- Hits       193716   193632     -84     
- Misses      41949    42001     +52     

[joncinque]

Just the micro-nit, the rest is great!