Modularize perf-dash code.

Currently perf-dash is huge, single package with all its code. It could benefit from being split into few smaller packages with more clearly defined responsibilities (downloader, parsers etc.) This way

Today I spent some time trying to split it into some packages, but failed as code has a lot of inter-dependencies.

It seems perf-dash is not going away anytime soon, so I think it'd be worth investing few hours in it. In turn this would allow adding new functionality (especially parsers more easily).

/area perf-dash

Start by examining the perf-dash package and mapping its inter-dependencies before proposing package boundaries. Consider responsibilities such as downloaders and parsers, then define what a successful refactor looks like: smaller packages with clearer responsibilities and an easier path for adding parsers.

Written by the indexing model from the issue text.