Feature: `plakar scan`

[brmzkw]

Currently, users lack visibility into the structure and size distribution of their importer contents before performing a backup.

We want to introduce a new subcommand, plakar scan, that inspects the contents of an importer. This command will help users analyze their data, identify large files, directories with many files, and generate visualizations like flamegraphs. The goal is to assist users in manually creating an exclusion list for the actual backup process.