Replication message de- / serialization

[adzialocha]

Implement Serialize and Deserialize traits for the basic replication message types: SyncRequest, Entry and SyncDone.

Closes #374

📋 Checklist

• Add tests that cover your changes
• Add this PR to the Unreleased section in CHANGELOG.md
• Link this PR to any issues it closes
• New files contain a SPDX license header

[codecov]

Codecov Report

Patch coverage: 76.53% and project coverage change: -0.39 ⚠️

Comparison is base (11744f7) 91.87% compared to head (ac031e1) 91.49%.

Additional details and impacted files

@@               Coverage Diff               @@
##           development     #375      +/-   ##
===============================================
- Coverage        91.87%   91.49%   -0.39%     
===============================================
  Files               75       77       +2     
  Lines             6710     6855     +145     
===============================================
+ Hits              6165     6272     +107     
- Misses             545      583      +38     

Impacted Files	Coverage Δ
aquadoggo/src/replication/message.rs	67.81% <67.81%> (ø)
aquadoggo/src/replication/mode.rs	70.58% <70.58%> (ø)
aquadoggo/src/replication/target_set.rs	90.90% <90.90%> (ø)
aquadoggo/src/replication/manager.rs	80.41% <100.00%> (-0.97%)	⬇️
aquadoggo/src/test_utils/helpers.rs	97.43% <100.00%> (+0.37%)	⬆️

... and 1 file with indirect coverage changes

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[sandreae]

Looks great!