Switch protocol framework to manul

[fjarri]

Fixes #151

As discussed in Slack, it's quite tricky to keep Presigning and Signing separate - if an error happens in Signing it requires a bunch of signed messages from Presigning, and it's very awkward to keep and supply them. So this PR merges Presigning and Signing.

If we ever need a separate Presigning, the 6-round version from the paper will be suitable, since its Signing counterpart does not require us to transfer any Presigning messages. See #36.

Even though the code is still kind of dirty, this PR is so huge I think it should just stop here. The cleanup will be made in subsequent PRs. We didn't introduce any new unfinished parts, all the unimplemented stuff has already been there before.

Update: the new version of CGGMP paper resolves this by moving all the required proofs into Presigning, but I would rather not modify this PR any more, and there's also another one stacked on top of it. The Presigning and Signing will be split again in the course of fixing #157

[codecov]

Codecov Report

Attention: Patch coverage is 84.42450% with 295 lines in your changes missing coverage. Please review.

Project coverage is 92.59%. Comparing base (844a7ea) to head (90ccb70).

Files with missing lines	Patch %	Lines
...drion/src/cggmp21/protocols/interactive_signing.rs	84.97%	148 Missing ⚠️
synedrion/src/cggmp21/protocols/key_refresh.rs	79.01%	47 Missing ⚠️
synedrion/src/cggmp21/protocols/aux_gen.rs	80.09%	41 Missing ⚠️
synedrion/src/cggmp21/protocols/key_init.rs	84.44%	28 Missing ⚠️
synedrion/src/www02/key_resharing.rs	86.09%	26 Missing ⚠️
synedrion/src/tools/hide_debug.rs	69.23%	4 Missing ⚠️
synedrion/src/cggmp21/entities.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #156      +/-   ##
==========================================
- Coverage   93.12%   92.59%   -0.53%     
==========================================
  Files          43       33      -10     
  Lines        8130     6661    -1469     
==========================================
- Hits         7571     6168    -1403     
+ Misses        559      493      -66     

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[dvdplm]

Fair enough!