Speedup audbackend.interface.Maven.ls()

[hagenw]

In its current implementation, the execution time of audbackend.interface.Maven.ls() scales with the content of the repository / sub-folder, as it first collects all files given under root or a sub-folder, and limits the results only afterwards for the requested file.

As all versioned belonging to a file are stored in the the sub-folder <root>/<name>/ there is no need for this. In this pull request, I use ls() of the underlying backend object to inspect the content of that folder and hence speed up the execution time.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.0%. Comparing base (bdc5368) to head (8aa9d92).

Additional details and impacted files

Files	Coverage Δ
audbackend/core/interface/maven.py	100.0% <100.0%> (ø)

[hagenw]

This is also the one advantage we have with the Maven interface, compared to the Versioned interface, as in Versioned we cannot limit the listing of files that easily.