Proper conversion to/from JS when issuing queries to Cassandra

Until now, values were only sporadically converted between rb-cassandra and Cassandra types. This PR resolves this, and systematically converts values from JS to Cassandra when issuing queries, and back to JS after fetching the result rows. It also introduces conversion schemes for set values whose underlying types need conversion (such as set<varint>, set<josn>, etc.).

This PR aims at resolving [T84900](https://phabricator.wikimedia.org/T84900)
> put a single function into a separate package

Ditto; I was thinking something more like `"cool-library-of-greatness": "1.0.0"`, which could include `identity()` among other useful functions and data structures that aren't overly specific to a particular project such as restbase.

Perhaps a good first step would be to factor these things out into *restbase/lib/thisShouldBeADependency.js*.  Then when that file starts to get big we can think about pulling it out into a proper module.