Assorted codebase fixes

[webbju]

Checklist

• I have read the Contributor Guide
• I have read and agree to the Code of Conduct
• I have added a description of my changes and why I'd like them included in the section below

Description of Changes

• Add source-level process timings; i.e. "how long did a specific file take to excise?" rather than purely global runtime.
• Remove custom CLI input path validation; Spectre.Console.Cli can do this via <INPUT_PATH> (angled bracket) syntax.
• Fix instance where namespace did not match project name.
• Fix confusing type casting when calculating "required excision ratio" from CLI percentage.