Handle checkout failure and propagate error message

[seer-by-sentry]

👋 Hi there! This PR was automatically generated by Autofix 🤖

This fix was triggered by Ido Shemesh.

Fixes ANDROID-10. The issue was that: Backend inventory validation failed for requested product quantity, causing a 500 response and triggering client-side error handling that threw an exception.

• Parse the error response from the checkout API to extract the error message.
• Propagate the error message to the processDeliveryItem method.
• Update processDeliveryItem to accept an error message parameter.
• Add a fallback error message if parsing fails.

If you have any questions or feedback for the Sentry team about this fix, please email autofix@sentry.io with the Run ID: 44902.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 22 lines in your changes missing coverage. Please review.

Project coverage is 0.00%. Comparing base (c211625) to head (00cffc3).

Files with missing lines	Patch %	Lines
.../example/vu/android/empowerplant/MainFragment.java	0.00%	22 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #173   +/-   ##
=====================================
  Coverage   0.00%   0.00%           
=====================================
  Files         15      15           
  Lines        780     795   +15     
  Branches      43      44    +1     
=====================================
- Misses       780     795   +15     

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