[EVM] Merge balances on associate tx

[stevenlanders]

Describe your changes and provide context

• adds new test that requires merge balances
• migrates balance from evm to sei when associating on sei tx

Testing performed to validate your change

• integration test

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 47.36842% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 61.46%. Comparing base (502a560) to head (d8bf2e1).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1630      +/-   ##
==========================================
- Coverage   61.48%   61.46%   -0.03%     
==========================================
  Files         366      366              
  Lines       26354    26360       +6     
==========================================
- Hits        16205    16203       -2     
- Misses       9069     9074       +5     
- Partials     1080     1083       +3     

Files	Coverage Δ
x/evm/ante/preprocess.go	76.69% <47.36%> (-1.01%)	⬇️

... and 4 files with indirect coverage changes