Fix AO loading when AO issue date is empty or null

[patphongs]

Summary

• Resolves AO does not load when issue_date is empty #6601

Handles advisory opinions when issue_date is empty or null.

This updates AO document sorting and date display so pages do not fail when a final opinion has no issue_date. In those cases, the AO page and AO search results display Not dated.

Required reviewers

1 engineer

Impacted areas of the application

General components of the application that this PR will affect:

• Advisory opinion individual pages
• Advisory opinion search results
• Advisory opinion table sorting

How to test

• Run pytest
  • test_sort_ao_documents_handles_missing_issue_date covers an AO with issue_date: None and a final opinion document, confirming document sorting does not fail.
  • test_advisory_opinion_page_handles_missing_issue_date covers an AO with issue_date: '' and a final opinion document, confirming the AO page renders and displays Not dated.
• Run npm run build-js

There does not appear to be an example in the current data of a final opinion with no issue_date. The new legal tests covers that case directly, including the document sorting in the AO table and final opinion date display on the individual AO page.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.73%. Comparing base (efe5dc3) to head (e24e5f6).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7197      +/-   ##
===========================================
+ Coverage    79.45%   79.73%   +0.27%     
===========================================
  Files          256      256              
  Lines         6738     6756      +18     
===========================================
+ Hits          5354     5387      +33     
+ Misses        1384     1369      -15     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.