feat: upgrade to v4

[0Tech]

Description

This PR upgrades the app version to v4-Marigold.

Checklist:

• I followed the contributing guidelines and code of conduct.
• I have added a relevant changelog to CHANGELOG.md
• I have added tests to cover my changes.
• I have updated the documentation accordingly.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 50.31%. Comparing base (de2cd06) to head (11aba00).

❗ Current head 11aba00 differs from pull request most recent head 53257f8. Consider uploading reports for the commit 53257f8 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #357   +/-   ##
=======================================
  Coverage   50.31%   50.31%           
=======================================
  Files          10       10           
  Lines        1407     1407           
=======================================
  Hits          708      708           
  Misses        654      654           
  Partials       45       45           

Files	Coverage Δ
app/app.go	83.87% <ø> (ø)
app/encoding.go	100.00% <ø> (ø)
cmd/fnsad/cmd/root.go	11.87% <ø> (ø)