add computing PublicKeyPackage from commitments

[conradoplg]

Allow computing PublicKeyPackage from commitments.

It also refactors a lot of related code which makes everything more organized.

Expanded from #502, I made a mess with the history after syncing with main and didn't want to force push in the contributor's PR.

[codecov]

Codecov Report

Attention: 7 lines in your changes are missing coverage. Please review.

Comparison is base (c0c57f4) 81.76% compared to head (c42f022) 81.94%.
Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #551      +/-   ##
==========================================
+ Coverage   81.76%   81.94%   +0.17%     
==========================================
  Files          30       30              
  Lines        3082     3151      +69     
==========================================
+ Hits         2520     2582      +62     
- Misses        562      569       +7     

Files	Coverage Δ
frost-core/src/batch.rs	100.00% <100.00%> (ø)
frost-core/src/frost.rs	92.44% <100.00%> (+0.08%)	⬆️
frost-core/src/frost/identifier.rs	98.64% <100.00%> (-0.12%)	⬇️
frost-core/src/frost/round2.rs	100.00% <100.00%> (ø)
frost-core/src/lib.rs	85.16% <100.00%> (ø)
frost-core/src/signing_key.rs	84.31% <100.00%> (ø)
frost-core/src/verifying_key.rs	98.52% <100.00%> (+0.34%)	⬆️
frost-core/src/frost/keys/dkg.rs	87.64% <95.52%> (-1.50%)	⬇️
frost-core/src/frost/keys.rs	97.75% <94.52%> (-0.66%)	⬇️

... and 1 file with indirect coverage changes

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[conradoplg]

Addressed comment

[conradoplg]

Last Rust also introduced some clippy issues so I went ahead and fixed them here.

[natalieesk]

Looks good