Characters endpoint performs poorly for plays with many characters

[cmil]

The performance of the /corpora/{corpusname}/plays/{playname}/characters endpoint degrades poorly for plays with a large number of characters. In the extreme case of https://dracor.org/api/v1/corpora/ger/plays/kraus-die-letzten-tage-der-menschheit/characters (925 characters) the request results in a gateway timeout. When requested directly from the eXist RESTXQ interface it takes more than 2min to complete.

While "Die letzten Tage der Menschheit" is certainly an edge case (Faust II with 189 characters still takes 10s), this performance issue currently makes the endpoint unusable for purposes like enhancing the network graphs (e.g. dracor-org/dracor-frontend#259).