fix: safely handle nonces as 64 bit uints

[wemeetagain]

Resolves #102

• Remove references to "uint32", which isn't in the spec and was misleading
• Check for a "max nonce" (Number.MAX_SAFE_INTEGER) when encrypting/decrypting
• Add comments describing the deviation from the spec, why it exists, and its effect

[codecov-commenter]

Codecov Report

Merging #118 (5f945a0) into master (61251ed) will decrease coverage by 0.02%.
The diff coverage is 90.47%.

@@            Coverage Diff             @@
##           master     #118      +/-   ##
==========================================
- Coverage   89.13%   89.11%   -0.03%     
==========================================
  Files          16       16              
  Lines        1831     1846      +15     
  Branches      243      245       +2     
==========================================
+ Hits         1632     1645      +13     
- Misses        199      201       +2     

Impacted Files	Coverage Δ
src/handshakes/abstract-handshake.ts	93.59% <90.47%> (-0.56%)	⬇️

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