Assorted fixes

[fjarri]

• Bump secrecy to the most recent stable version (0.10) (this is an internal change)
• Bump crypto-bigint to 0.6-rc.6 and crypto-primes to 0.6.0-pre.2 (this is an internal change)
• Remove unused base64 dependency and move hex to dev-dependencies (should have been done in Switch to serde-encoded-bytes #153)
• Remove the need for getrandom/js dependency (crypto-primes's default features were requiring it, but we don't need those features)
• Remove an explicit Debug for SecretKeyPaillier - derivation works well enough
• Remove unncecessary Zeroize and ZeroizeOnDrop derivations (don't need Zeroize if ZeroizeOnDrop is already derived, and don't need ZeroizeOnDrop in structs that already have all secret data in SecretBox)

[codecov]

Codecov Report

Attention: Patch coverage is 96.15385% with 1 line in your changes missing coverage. Please review.

Project coverage is 93.14%. Comparing base (6bac5fa) to head (00ebe53).
Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
synedrion/src/paillier/keys.rs	96.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #155      +/-   ##
==========================================
+ Coverage   93.13%   93.14%   +0.01%     
==========================================
  Files          43       43              
  Lines        8124     8130       +6     
==========================================
+ Hits         7566     7573       +7     
+ Misses        558      557       -1     

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