Remove napari_hook_implementation decorator

[jni]

• Remove a remnant napari_hook_implementation from get_writer
• Update python versions in setup.cfg

Closes #31

please fix test matrix

[jni]

Thanks @Czaki! I've gone with the strategy of only testing earliest and latest python.

[jni]

@Czaki I dropped this. Just found it again by going through my open PRs. Can you please sanity-check it before I merge? 🙏

[andy-sweet]

Seems fine to me. What's the motivation behind not testing the Python versions in the middle? Avoiding overkill? The tests seem to run pretty quickly, so doesn't seem to necessary, but I also don't oppose.

[jni]

yeah we do that in the napari repo I think? Anyway, someone at some point suggested that this was a good strategy and I agree. It seems exceedingly unlikely that code would run in .9 and .12 but not in the middle...