feat(docs): upgrade-bn

[danforbes]

Add a section in "Upgrade from 1.x" for BN vs BigInt

Closes #6705

[github-actions]

Bundle Stats

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Total

Files count	Total bundle size	% Changed
10	639.17 kB	0%

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No files were changed

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Bigger

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Unchanged

Asset	File Size	% Changed
web3.min.js	619.88 kB	0%
../lib/commonjs/index.d.ts	8.69 kB	0%
../lib/commonjs/accounts.d.ts	3.89 kB	0%
../lib/commonjs/types.d.ts	2.67 kB	0%
../lib/commonjs/web3.d.ts	1.35 kB	0%
../lib/commonjs/web3_eip6963.d.ts	1.2 kB	0%
../lib/commonjs/abi.d.ts	999 B	0%
../lib/commonjs/eth.exports.d.ts	280 B	0%
../lib/commonjs/providers.exports.d.ts	183 B	0%
../lib/commonjs/version.d.ts	60 B	0%

[github-actions]

Benchmark

Benchmark suite	Current: 9e02d00	Previous: 9b32205	Ratio
processingTx	21476 ops/sec (±7.25%)	23392 ops/sec (±7.52%)	1.09
processingContractDeploy	38912 ops/sec (±7.62%)	40479 ops/sec (±6.69%)	1.04
processingContractMethodSend	15657 ops/sec (±7.30%)	16317 ops/sec (±6.87%)	1.04
processingContractMethodCall	27034 ops/sec (±8.19%)	27614 ops/sec (±8.40%)	1.02
abiEncode	42844 ops/sec (±6.90%)	46686 ops/sec (±6.17%)	1.09
abiDecode	30842 ops/sec (±7.22%)	31121 ops/sec (±7.84%)	1.01
sign	1548 ops/sec (±0.86%)	1556 ops/sec (±0.91%)	1.01
verify	362 ops/sec (±0.61%)	369 ops/sec (±0.48%)	1.02

This comment was automatically generated by workflow using github-action-benchmark.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.50%. Comparing base (9b32205) to head (9e02d00).
Report is 2 commits behind head on 4.x.

Additional details and impacted files

@@           Coverage Diff           @@
##              4.x    #7232   +/-   ##
=======================================
  Coverage   94.50%   94.50%           
=======================================
  Files         216      216           
  Lines        8429     8429           
  Branches     2315     2315           
=======================================
  Hits         7966     7966           
  Misses        463      463           

Flag	Coverage Δ
UnitTests	94.50% <ø> (ø)

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