[FEATURE] Enhance `core_pan` module

[cb-Hades]

The core_pan module contains some rudimentary functions for building and comparing core-pan models with other models. Extending this model would enable better curation of core-pan models and meaningful analysis of the core-pan content of other models.

Discussion Points

1. Entity comparison

ISSUE:
Currently, the similarity of model entities is solely determined by the model IDs, which can be rather problematic as models do not necessarily use the same IDs/namespace. This is further complicated because even a namespace might change over time.

IDEAS:

• comparison based on (single) database IDs/annotations
• similarity search with a similarity cut-off (multi-annotation / feature search)

[dyrpsf]

Hi @cb-Hades and @draeger,

I have opened PR #189 to address this.
I extended the core_pan module to support annotation-based entity comparisons, including a fallback to standard model IDs to prevent data loss.

Ready for review whenever you have a minute!