ENH: Add public types to the package.

[tobiasraabe]

Is your feature request related to a problem?

#160 added rudimentary typing to the package.

What is still missing are public types which can be used in plugins and other code to validate functions.

Describe the solution you'd like

Add types to the public interface. Here is a list of published types:

Additional context

• https://github.com/pytest-dev/pytest/issues/7469 is the main issue describing typing in pytest.

[tobiasraabe]

For a first shot, try to type https://github.com/tobiasraabe/software_patents and see what issues come up.

[tobiasraabe]

It would be super cool if we could enforce that all hook implementations follow the types of the hook specifications. Here are some hints how to accomplish it:

• https://stackoverflow.com/questions/54674679/how-can-i-annotate-types-for-a-pluggy-hook-specification
• https://github.com/pytest-dev/pluggy/issues/191