fix(je-1333): ajusta formato do message cover para utilizar classe pura

[renanlucaz]

Descrição

A lib estava retornando um erro ao instanciar a capa de mensageria no arquivo message_builder.py, pois não reconhecia a biblioteca pydantic. A solução foi alterar o formato para utilizar apenas a classe pura, sem dependência do pydantic.

Testes rodando

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.09%. Comparing base (663f19a) to head (fcfeb60).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #40      +/-   ##
==========================================
+ Coverage   94.95%   95.09%   +0.13%     
==========================================
  Files          25       25              
  Lines         972      979       +7     
==========================================
+ Hits          923      931       +8     
+ Misses         49       48       -1     

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