Mixin class

[CBroz1]

Description

Initial implementation of Mixin class is added to any table with an existing fetch_nwb, allowing special cases to override. Mixin uses table definition to decide which table to use. If none is in definition, class must have a table attribute. Is this enough to allow all tables to have the mixin, without tables inadvertently accessing the method?

Checklist:

• This PR should be accompanied by a release: (yes/no/unsure)
• (If release) I have updated the CITATION.cff
• I have updated the CHANGELOG.md
• I have added/edited docs/notebooks to reflect the changes

[edeno]

I think this general structure makes sense. I wonder if there could be a more informative name of the mixin (SpyglassMixin doesn't exactly tell you what it is doing), but I guess the class is broad enough (fetch nwb, delete) that Spyglass is okay.

[CBroz1]

more informative name

I agree. Happy to rename if you have something else in mind, but I figured it would grow in responsibility over time - fetch_nwb and permission-restricted delete are already diverse enough responsibilities that I thought they would need separate mixins if we wanted informative names

[rly]

I think this is a good idea and will clean up a good amount of code. However, a minor suggestion - I think the class variable nwb_table should start with an underscore or even two, to warn people not to mess with it, e.g., with StateScriptFile.nwb_table = X