[texodus]

This PR adds support for multiple index columns to Table:

client.table(data, {index: ["Book", "Security"]});

Internally, this feature uses a non-utf8, order-preserving, type-aware binary encoding packed in a t_tscalar::string, which itself is memoized in a dictionary. This slightly improves performance by avoiding e.g. datetime stringification, but the real impact is API support - for streams that need multiple index support, you no longer need to decode + stringify + concat + encode these columns to inject them into Perspective, ideally avoiding encode/decode entirely if the source emitter support Arrow.

Multi-index support is backwards compatible, string arguments to index still work and are identical to an array with a single string.