deprecate passing classes as hookspecs, it shold be instances

[RonnyPfannschmidt]

we currently have self magic in place to handle unbound methods and passed in classes

ass signature (see #359) handles the bound methods so much better, we should ensure hook-specs are instances not types, and then generally handle them that way

followup to https://github.com/pytest-dev/pluggy/pull/359#discussion_r936410218_

[nicoddemus]

Currently many hookspecs are actually modules... is the plan to force to move hookspec functions to methods of a class?

[RonnyPfannschmidt]

@nicoddemus modules will still be allowed, but passing classes would be disallowed, instead they'd have to be instances (orf control of method vs bound method

it may be permissible to allow types that don't take arguments

[nicoddemus]

Currently we support modules, classes or instances, the plan is to support only modules or instances. Got it, thanks.