Transition JAX entropy coders to a project

[mmuckley]

Enhancement

Transition all JAX entropy coders to a folder under projects.

Motivation

These were originally released to be the basis of work incorporating neural networks into codecs, but so far adoption for this task has been a little light, rendering them more of a proof-of-concept. JAX in particular has a heavier install and start-up process, so it might be nice to have these as a project with more finely-scoped dependencies.

Alternatives

We could change nothing and leave the entropy coders where they are.