hooks: add hook for pynput

[eric15342335]

Pynput chooses different backends for different platforms, but users can specify via environment variables too.

I am not sure if this is right.

[eric15342335]

or we can use alternative method like how pynput detects backend

[bwoodsend]

Hmm, what we're trying to with the matplotlib hook (which also has a choice of backends) is make the selection configurable. In this case it would be to have whatever backend pynput selects by default as the default then have a hook option to choose a backend (or possibly backends if needing more than one is likely?).

[bwoodsend]

Actually looking at their available backends, this isn't really like matplotlib where you have more choices than you need, it's pretty much just one per OS meaning that your collect_submodules() approach is fine.

[bwoodsend]

It does have per-platforn dependencies (python-xlib for Linux, pyobjc-framework-Quartz for macOS`) which will likely become warnings on other OSs because they're not installed.

[bwoodsend]

Here's CI and some more CI becuase Linux needs a virtual screen.

[bwoodsend]

Cheers @eric15342335!