Handle JUnit <error> result state in parse_testcase()

[patdhlk]

Summary

Fixes #132

• parse_testcase() now explicitly handles the JUnit <error> element, which represents unexpected exceptions or infrastructure crashes
• Previously, <error> test cases were silently classified as "passed" (false-positive verdict)
• Adds CSS styling for the tr_error result type (orange, distinct from failure red and skip gray)
• Also guards against None text in <failure> elements (consistency with the <skipped> branch)

Changes

• sphinxcontrib/test_reports/junitparser.py — Add elif hasattr(testcase, "error") branch before the else clause
• sphinxcontrib/test_reports/css/common.css — Add tr_error row and status badge styles
• tests/doc_test/utils/xml_data_error.xml — New test fixture with all four result states
• tests/test_junit_parser.py — New test_parse_error_xml() covering error parsing

Test plan

• New test_parse_error_xml verifies error result, type, message, and text extraction
• All 31 existing tests continue to pass
• No changes to rendering logic needed — existing "tr_" + result pattern handles the new state automatically

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.50%. Comparing base (529246a) to head (20764c0).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #134      +/-   ##
==========================================
+ Coverage   84.16%   84.50%   +0.33%     
==========================================
  Files          26       26              
  Lines        1295     1323      +28     
  Branches      156      157       +1     
==========================================
+ Hits         1090     1118      +28     
  Misses        134      134              
  Partials       71       71              

☔ View full report in Codecov by Sentry.
📢 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.