Function measureTexts

The bits of the texts of a link, by their group, e.g. to tell an author which texts make a link long: of each group the bits of its references, and its share of the block of the strings.

The block is compressed by a model that learns while it codes, so what a string costs depends on the strings before it, and no split of the block is exact. This one is fair: the Shapley value. The block is encoded with the texts of each subset of the groups; the share of a group is what adding it saves, averaged over all the orders in which the groups could be added. The shares add up to the bits of all texts; what two groups have in common, e.g. words that both use, is split evenly between them; a text used in two groups is in a subset if one of them is.

The groups add up to less than the kinds strings and stringRefs of measureLink: the rest are the words of the format (e.g. the names of symbols and fonts), the number of strings and the end of the block. Shares are fractions of bits. A map with up to 4 groups encodes the block up to 16 times, which takes some milliseconds for a map of hundreds of texts. Throws like decodeState if the link cannot be read.