all: cleanup repairable module

[conradoplg]

Based on #922, which needs to be merged before this

Closes #951

[codecov]

Codecov Report

❌ Patch coverage is 42.73504% with 67 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.37%. Comparing base (504ef20) to head (2585bd2).

Files with missing lines	Patch %	Lines
frost-core/src/keys/repairable.rs	79.36%	13 Missing ⚠️
frost-ed25519/src/keys/repairable.rs	0.00%	9 Missing ⚠️
frost-ed448/src/keys/repairable.rs	0.00%	9 Missing ⚠️
frost-p256/src/keys/repairable.rs	0.00%	9 Missing ⚠️
frost-ristretto255/src/keys/repairable.rs	0.00%	9 Missing ⚠️
frost-secp256k1-tr/src/keys/repairable.rs	0.00%	9 Missing ⚠️
frost-secp256k1/src/keys/repairable.rs	0.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #957      +/-   ##
==========================================
- Coverage   77.45%   77.37%   -0.09%     
==========================================
  Files          41       41              
  Lines        4503     4540      +37     
==========================================
+ Hits         3488     3513      +25     
- Misses       1015     1027      +12     

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