Temporary directories created during remote proxy (when build was suddenly suspended in the middle of downloading artifacts) are not cleaned up

To reproduce this issue:

1. Using the default configuration with repository 'internal' proxying 'central', set repository 'internal' as your mirror. Lock Maven to use only this with <mirrorOf>*</mirrorOf>
2. Clean up your local repository

• Build any project. In the middle of a download, disable your internet connection.

Notice that the temporary working directory (ex. .workingdirectory4849954836595460673.tmp) is present in repository 'internal'. Try enabling your net connection again and build your project. The temporary working directory in 'internal' created from your previous download would still be there even after your project has already been built.

This should be cleaned up after a certain time has passed during proxying or by a clean up consumer/plugin.