[client] exclude src_ref and dst_ref handling in import_observable (#14597)

[JeremyCloarec]

Proposed changes

• exclude src_ref and dst_ref handling in import_observable. They are already handled directly in observable creation in opencti_stix_cyber_observable's create

Related issues

• fix Error "Cant add another relation on single ref" with a bundle that contains IPv4 address and NetworkTraffic #14597

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case (coverage and e2e)
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality

Further comments

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 32.37%. Comparing base (0f1ee38) to head (d20838f).
⚠️ Report is 24 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #14666   +/-   ##
=======================================
  Coverage   32.36%   32.37%           
=======================================
  Files        3096     3096           
  Lines      210905   210968   +63     
  Branches    38201    38213   +12     
=======================================
+ Hits        68269    68297   +28     
- Misses     142636   142671   +35     

Flag	Coverage Δ
opencti-client-python	45.50% <ø> (ø)
opencti-front	2.83% <ø> (+<0.01%)	⬆️
opencti-graphql	67.73% <ø> (-0.01%)	⬇️

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[Copilot]

Pull request overview

Adjusts the Python client STIX2 import logic to avoid creating duplicate nested-ref relationships for Network-Traffic src_ref / dst_ref, which can trigger the “Cant add another relation on single ref” error when importing bundles containing NetworkTraffic + IP observables.

Changes:

• Excludes src_ref and dst_ref from the generic “iterate over refs and create nested relationships” loop in import_observable.

[Copilot]

This change fixes a specific import path (Network-Traffic src_ref/dst_ref), but there’s no unit/integration test ensuring import_observable does not call stix_nested_ref_relationship.create for these keys anymore. Adding a regression test with a mocked api_client/opencti that imports a Network-Traffic observable (with src_ref/dst_ref) and asserts only the observable creation is performed would prevent reintroducing the "Cant add another relation on single ref" error.