Format option proposal: `pkgname-coverage-graph`

I like to work with coverage, and I think it would be a great addition to have an output format, that would help identify which packages are badly covered, at a glance.

The format would be based on the existing `pkgname` one. Here is an example of what it could look like:


Thoughts about the global idea ? I drafted the presentation and colors so it might be improved. I like the more graphical aspect for coverage. It could also work easily when coverage is not enabled:


The end of the input could look like `pkgname`. A line could also show the global test coverage.

Start by reviewing the existing `pkgname` output format and how coverage results are presented. Clarify the proposed graph layout, colors, input ending, and global coverage line before implementation. Done means an agreed `pkgname-coverage-graph` format that also behaves sensibly when coverage is disabled.

Written by the indexing model from the issue text.