feat: add serde to mempool messages

[Itay-Tsabary-Starkware]

This change is 

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.

Project coverage is 78.21%. Comparing base (5a6f61a) to head (189ddbc).
Report is 1 commits behind head on main.

Files	Patch %	Lines
crates/mempool_types/src/mempool_types.rs	0.00%	4 Missing ⚠️
crates/mempool_types/src/communication.rs	0.00%	2 Missing ⚠️
crates/mempool_types/src/errors.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #277      +/-   ##
==========================================
- Coverage   78.60%   78.21%   -0.40%     
==========================================
  Files          26       27       +1     
  Lines        1192     1198       +6     
  Branches     1192     1198       +6     
==========================================
  Hits          937      937              
- Misses        201      207       +6     
  Partials       54       54              

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