fix(segment-update): handle rules/conditons without id correctly

[gagantrivedi]

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Changes

Overwrite the __init__ method to handle deletion of rules/conditions correctly. The earlier implementation was overriding get_initial, but since WritableNestedModelSerializer uses that internally, it resulted in some strange behavior where rules/conditions that should have been created or updated were instead removed.

How did you test this code

Adds unit tests

[vercel]

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3 Skipped Deployments

Project	Deployment	Preview	Comments	Updated (UTC)
docs	Ignored	Preview		Aug 21, 2025 9:34am
flagsmith-frontend-preview	Ignored	Preview		Aug 21, 2025 9:34am
flagsmith-frontend-staging	Ignored	Preview		Aug 21, 2025 9:34am

[github-actions]

Docker builds report

Image	Build Status	Security report
ghcr.io/flagsmith/flagsmith-api-test:pr-5953	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-e2e:pr-5953	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-api:pr-5953	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-frontend:pr-5953	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith:pr-5953	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-private-cloud:pr-5953	Finished ✅	Results ✅

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.86%. Comparing base (0dcd073) to head (898e1d1).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5953   +/-   ##
=======================================
  Coverage   97.86%   97.86%           
=======================================
  Files        1275     1275           
  Lines       45227    45267   +40     
=======================================
+ Hits        44261    44301   +40     
  Misses        966      966           

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[Zaimwa9]

👏 Sorry, couple of comments. Being a bit annoying just to close the topic once and for all

[Zaimwa9]

👍