v6.19

Fixes an issue where the bud.module cache was not properly invalidated, resulting in import errors when upgrading from earlier versions (#2523).

This release reverts the figures dependency to v4 to maintain compatibility with Node 16. We will do this upgrade when we release the next major version of bud.js, and recommend all users move on to Node 20 as soon as possible. Still, we didn't intend to introduce this incompatibility in a minor release (v6.18.0).