[FEAT] add file complexity

[DerTimonius]

Description

The output with the -a or -t flag collects information about both file length and number of commits. Both could be combined to calculate the complexity or importance of a file. A smaller file that is changed often might be more important to a project than a large file that is only changed once per year.

Technical Details

• add a function in impl File in file.rs that calculates the complexity
• add the complexity to the tables in the grouped_info function
• possibly also add an option to only display the complexity (needs a new flag in the clap command, and a new display function)