Update dependencies (fixes vulnerability in Jinja v3.1.3)

Security

• update Jinja2 dependency (again) to fix security vulnerability

Changed

• rename some DirWalk parameters
• add unit tests for DirWalk class
• run slow tests when all other tests have passed
• refactor code
• change directory layout of source code

Fixed

• fix: no files are included in case no suffixes are specified
• fix: excluded file names cannot use globs
• fix: poetry cannot find root folder