Refactoring: package managers: pip: tracker

[eskultety]

This is the main refactoring tracker for the pip package manager module.

The list will be updated as necessary.

• [ ] Convert PipRequirement._assess_direct_access_requirement to a static helper method instead of a class method
• [ ] Convert PipRequirement._split_hashes_from_options to a static helper method instead of a class method
• [ ] Enable typing for PipRequirement.from_line class method
• [ ] Make PipRequirement a subclass of packaging.Requirement
• [ ] Break the module's functionality into several logical modules contained in a subpackage (see the Yarn subpackage and modules for inspiration)

[eskultety]

Closing in favour of https://github.com/containerbuildsystem/cachi2/milestone/1 which suits the notion of a tracker better.