Convert all HashMaps to BTreeMaps

[natalieesk]

This closes #476

[github-actions]

Visit the preview URL for this PR (updated for commit 2370b44):

https://frost-book--pr547-hashmap-to-btreemap-plywv6ar.web.app

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[codecov]

Codecov Report

Patch coverage: 29.82% and project coverage change: -0.02% ⚠️

Comparison is base (a5dc479) 81.43% compared to head (2370b44) 81.42%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #547      +/-   ##
==========================================
- Coverage   81.43%   81.42%   -0.02%     
==========================================
  Files          30       30              
  Lines        3027     3025       -2     
==========================================
- Hits         2465     2463       -2     
  Misses        562      562              

Files Changed	Coverage Δ
frost-ed25519/src/keys/dkg.rs	0.00% <0.00%> (ø)
frost-ed25519/src/keys/repairable.rs	59.09% <0.00%> (ø)
frost-ed25519/src/lib.rs	64.06% <0.00%> (ø)
frost-ed448/src/keys/dkg.rs	0.00% <0.00%> (ø)
frost-ed448/src/keys/repairable.rs	59.09% <0.00%> (ø)
frost-ed448/src/lib.rs	64.06% <0.00%> (ø)
frost-p256/src/keys/dkg.rs	0.00% <0.00%> (ø)
frost-p256/src/keys/repairable.rs	59.09% <0.00%> (ø)
frost-p256/src/lib.rs	68.27% <0.00%> (ø)
frost-ristretto255/src/keys/dkg.rs	0.00% <0.00%> (ø)
... and 10 more

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[conradoplg]

Looks good, thank you!