fix(checkout): guard invalid carrier settings

[NabDevs]

Prevents the checkout from crashing when carrier settings are missing or invalid. In that case, the delivery options service uses the default package type and returns no carriers. Includes regression coverage for missing and malformed settings.

Relates to: Woo PR

fixes INT-1730

[Copilot]

Pull request overview

This PR hardens the checkout delivery options flow against missing/invalid carrier settings so the checkout doesn’t crash and instead falls back to the default package type while exposing no carriers.

Changes:

• Added a guard in DeliveryOptionsService::getValidCarrierOptions() to early-return when carrier settings are missing/invalid.
• Added a regression test matrix for missing/invalid carrier settings.
• Updated an existing delivery options config unit test to explicitly store enabled carrier settings for PostNL.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/App/DeliveryOptions/Service/DeliveryOptionsService.php	Adds an early-return fallback when carrier settings are empty/invalid to prevent checkout crashes.
tests/Unit/App/DeliveryOptions/Service/DeliveryOptionsServiceInvalidCarrierSettingsTest.php	Introduces regression coverage for invalid carrier settings inputs.
tests/Unit/App/Context/Model/DeliveryOptionsConfigTest.php	Ensures carrier settings exist/enabled so config expectations remain valid with the new guard behavior.

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[codecov]

Codecov Report

❌ Patch coverage is 88.23529% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.34%. Comparing base (82a9650) to head (3f415a2).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
.../Carrier/Service/CapabilitiesValidationService.php	75.00%	1 Missing ⚠️
...tings/Repository/AbstractPdkSettingsRepository.php	85.71%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #513      +/-   ##
============================================
+ Coverage     94.32%   94.34%   +0.02%     
- Complexity     2409     2443      +34     
============================================
  Files           352      352              
  Lines          7716     7782      +66     
============================================
+ Hits           7278     7342      +64     
- Misses          438      440       +2     

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