Update Cube Values (batch)

Submit multiple matrix publishes in one request. Batch-level message, currency, and metadata apply to the whole run; each element of publishes contains a matrix (and optional per-publish metadata). Publishes are processed in order in the background. A batch may contain at most 50 publishes. Overlapping subcubes between any two publishes are rejected with 400. Optional per-publish metadata.Range sets the range label in the completion email (same key family as Document, Sheet, Software, URL, Publish Currency, Range); otherwise the server uses Range {index}.