refactor: always treat nonce as BigNumber

[faustbrian]

Resolves #195

[codecov]

Codecov Report

Merging #200 into master will increase coverage by 0.49%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #200      +/-   ##
==========================================
+ Coverage   81.56%   82.05%   +0.49%     
==========================================
  Files          26       24       -2     
  Lines         743      624     -119     
  Branches       92       77      -15     
==========================================
- Hits          606      512      -94     
+ Misses        136      111      -25     
  Partials        1        1              

Impacted Files	Coverage Δ
src/services/identity/address.ts	79.16% <0.00%> (-8.84%)	⬇️
src/services/identity/public-key.ts	81.25% <0.00%> (-8.75%)	⬇️
src/services/identity/private-key.ts	90.00% <0.00%> (-3.34%)	⬇️
src/services/message.ts	94.11% <0.00%> (-1.34%)	⬇️
src/utils/crypto.ts
src/utils/hash.ts
src/dto/transaction.ts	90.47% <0.00%> (+0.23%)	⬆️
src/services/client.ts	86.11% <0.00%> (+2.21%)	⬆️
src/services/transaction.ts	61.94% <0.00%> (+2.74%)	⬆️
src/services/identity/keys.ts	94.11% <0.00%> (+9.11%)	⬆️

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