Can't tell which file pipreqs is getting its packages from

I have a large project and `pipreqs` seems to be generating too many packages. I want to know which Python file is resulting in which packages to be found by `pipreqs`. I tried doing file by file, but apparently `pipreqs` doesn't support a single file for input either, just entire directories.

There should be a way to see which exact Python file yielded which required packages.

Start by reviewing how pipreqs accepts a directory and discovers imports across its Python files. Define an output that maps each source file to the packages it contributes, then verify it on a project where the generated requirements currently include unexpected packages.

Written by the indexing model from the issue text.