Support method-level coverage in Cobertura XML files

As per an enlightening discussion with @nedbat on a Discord thread, coverage.py already reports on function and class coverages. This is achieved through HTML reports, in which we can see "Files, Functions, Classes" at the top of the index page.

However, the (Cobertura) XML report doesn't expose the same information. Instead, the coverage.py's xml report will show empty <methods/> entries

My feature request is to populate the the XML report with the function/methods coverage info. A sample XML on how the content should look like can be seen here

This feature would be helpful for rendering tools to easily report on/parse coverage information and possibly fail CI/CD runs when coverage is low for at the method-level coverage.

As a side note - but probably unrelated to the request, is that another project named fun-coverage implemented method-coverage on terminal-only.

Start by tracing coverage.py's Cobertura XML report generation and compare it with the HTML report's function and class coverage data. Review the linked Cobertura sample to determine the expected method structure. Done means the XML report contains method-level coverage information and existing report behavior remains covered by tests.