feat: make duration_seconds optional

[joseph-sentry]

also adds a test for a JUnit XML that only has a single empty testsuites tag

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 85.34%. Comparing base (3348c31) to head (2443547).
Report is 9 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/testrun.rs	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #46      +/-   ##
==========================================
- Coverage   87.50%   85.34%   -2.16%     
==========================================
  Files           5        5              
  Lines         568      587      +19     
==========================================
+ Hits          497      501       +4     
- Misses         71       86      +15     

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

[codecov-notifications]

Codecov Report

Attention: Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/testrun.rs	88.88%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!