ckks: reference for barrett reduction

[j2kun]

In re #95

Add a link to a reference implementation of Barrett reduction, and connect the precomputed constants to the reference, and then document any parts of the impl that differ for TPU- or BAT-specific reasons

[github-actions]

This issue has 2 outstanding TODOs:

• jaxite/jaxite_ckks/barrett.py:56: Document with a reference
• jaxite/jaxite_ckks/barrett.py:88: Document with a reference

This comment was autogenerated by todo-backlinks