chore: use web3-utils instead of bignumber.js

[Hugoo]

Let's save 18.2kb as this feature is already included in web3-utils

[codecov-commenter]

Codecov Report

Merging #304 (0349a7b) into develop (122efa9) will increase coverage by 0.82%.
Report is 59 commits behind head on develop.
The diff coverage is 89.59%.

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@@             Coverage Diff             @@
##           develop     #304      +/-   ##
===========================================
+ Coverage    83.04%   83.86%   +0.82%     
===========================================
  Files           18       18              
  Lines          979     1122     +143     
  Branches       218      252      +34     
===========================================
+ Hits           813      941     +128     
- Misses          91       97       +6     
- Partials        75       84       +9     

Files Changed	Coverage Δ
src/lib/getData.ts	89.79% <ø> (ø)
src/lib/provider-wrapper-utils.ts	88.88% <ø> (-0.59%)	⬇️
src/lib/decodeMappingKey.ts	84.21% <60.00%> (-5.54%)	⬇️
src/lib/utils.ts	83.12% <76.92%> (-0.77%)	⬇️
src/lib/decodeData.ts	81.81% <83.33%> (+0.91%)	⬆️
src/provider/providerWrapper.ts	81.25% <90.00%> (-1.65%)	⬇️
src/lib/encoder.ts	83.95% <91.66%> (+6.04%)	⬆️
src/constants/constants.ts	100.00% <100.00%> (ø)
src/constants/interfaces.ts	100.00% <100.00%> (ø)
src/index.ts	76.76% <100.00%> (-0.24%)	⬇️
... and 2 more

... and 4 files with indirect coverage changes