pipreqs not recognizing pycairo

I have an `import cairo` call in one of my .py files in my project. Running `pipreqs --force` does not result in a requirements.txt file containing pycairo.

Start by tracing how pipreqs maps the `import cairo` name to a package when running `pipreqs --force`. Check the existing import-to-distribution data and related behavior, then verify that a generated requirements.txt includes `pycairo` for a project containing that import.

Written by the indexing model from the issue text.