Fixes and refactor

• run clippy
• better use of serde_json
• use Result<> instead of unwrap()
• remove pub from main.rs
• remove unused code read_lines
• filter paths by components instead of grepping in entire path (fixes a bug in --list for 'neon')

When running

REPOS=../../kde/invent/ REPO_METADATA=../repo-metadata/ cargo run -- --branch-group kf6-qt6  > kf6-qt6-master

two more projects are listed:

$ diff kf5-qt5-list-master kf6-qt6-list-fixes
541a542
> rolisteam/rolisteam-packaging master
605a607
> system/ubiquity-slideshow-neon master