Changes

Refactors Story entity constructors and dataset initialization
Updated the Story constructors to accept a collection of themes instead
of varargs and added a new constructor that includes id and publishedAt
for easier dataset creation. Ensured that a story cannot be created
without themes. The StoriesDataset class was refactored to use these new
constructors, simplifying story initialization by removing repetitive
calls to setId and setPublishedAt. Minor typos and formatting issues in
story content were also corrected.