Add support for processing junit4 reports from TEST-junit-vintage.xml

[stefanwatt]

Content:

• spec_builder now just returns the reports_dir instead of a path to a file
• result_builder now builds results for all the possible report files

[stefanwatt]

To be honest I don't know how to run the lua tests locally. Should it "just work" with neotest?

[rcasia]

The approach was correct. I just made some adjusments:

• fixed the formatting
• read all the files in the report_dir so if the name changes it still reads it.

Thanks for all and sorry for my late response!