Investigate caching changes in AiiDA v2

[danielhollas]

Recent versions of aiida-core saw fair amount of improvements and changes to caching. We need to investigate how these changes interact with the fixtures in this package.

[danielhollas]

Note to self: Need to understand how this package utilizes cache and its invalidation.

For example, until 2.6, the cache was invalidated for each aiida-core version. Was that handled somehow here, or did users need to recreate the data when if they bumped aiida-core?

[ltalirz]

this is something @janssenhenning might know

[danielhollas]

Note that 2.6 also introduced a cache invalidation mechanism that is very important to note about for plugin developers. We should mention it in the docs.

https://aiida.readthedocs.io/projects/aiida-core/en/v2.6.0/topics/provenance/caching.html#calculation-jobs-and-parsers