Explainability support

[mtanghu]

Some original ideas will likely be needed, but in general this should be achievable simply through measuring the dot-product similarities of F1 and F2 (and also softmaxing them) to see what tokens the model is paying attention to, then factor in the querying aspect.

A good entry point would be to reproduce a variation of the pairwise Attention diagram found in the appendix of Attention is All you Need