An array of MultiZetaStimulus objects representing the corpora to validate.
This function takes an array of MultiZetaStimulus objects, where each
object represents an item containing item parameters (zetas) associated with
different CAT models. The function checks for any duplicate cat names across
each item's array of zeta values. It throws an error if any are found.
Validates a corpus of multi-zeta stimuli to ensure that no cat names are duplicated.