refactor(server): extract shared response builder code

[pedro-avalos]

Description

• This PR extracts duplicated code in the server's response building logic

Related Issue(s)

Untracked

Testing

• Unit tests

Checklist

• I have followed the contribution guidelines.
• I have signed the Canonical CLA.
• I have added necessary tests.
• I have added or updated any relevant documentation (if needed).
• I have tested the changes.

Additional Notes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.28%. Comparing base (26ecee3) to head (f49e2f7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #514      +/-   ##
==========================================
+ Coverage   89.20%   89.28%   +0.07%     
==========================================
  Files          28       28              
  Lines        1389     1418      +29     
  Branches        1        4       +3     
==========================================
+ Hits         1239     1266      +27     
- Misses        150      151       +1     
- Partials        0        1       +1     

Flag	Coverage Δ		*Carryforward flag
charm	100.00% <ø> (ø)		Carriedforward from 26ecee3
client	80.24% <ø> (ø)		Carriedforward from 26ecee3
server	96.99% <ø> (-0.04%)	⬇️	Carriedforward from 26ecee3

*This pull request uses carry forward flags. Click here to find out more.

Components	Coverage Δ
Server	96.86% <100.00%> (+<0.01%)	⬆️
Charm	97.10% <ø> (-2.90%)	⬇️
Client	80.24% <ø> (ø)

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