feat: migrate ethers to v6

[sebastiendan]

Description

This PR updates ethers to v6.

Fixes TOO-395

PR Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added or updated tests that comprehensively prove my change is effective or that my feature works

[codecov]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (bb9221a) 87.44% compared to head (1352470) 87.64%.

Files	Patch %	Lines
packages/frontend/src/hooks/useReceiptTrie.ts	89.28%	3 Missing ⚠️
packages/frontend/src/hooks/useRegisterToken.ts	94.44%	1 Missing ⚠️
packages/frontend/src/hooks/useRegisteredTokens.ts	96.15%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #41      +/-   ##
==========================================
+ Coverage   87.44%   87.64%   +0.20%     
==========================================
  Files          27       26       -1     
  Lines        1282     1271      -11     
  Branches      130      124       -6     
==========================================
- Hits         1121     1114       -7     
+ Misses        161      157       -4     

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