feat: 🎸 store the rows content as a JSON string
For the new splits stored in the cache database, the rows content are
converted to a JSON string. The return type of get_rows_response has
changed: it's a 4-tuple, with optional json_content_rows and
content_rows.

BREAKING CHANGE: 🧨 return type of get_rows_response has changed
feat: 🎸 store the rows content as a JSON string: For the new splits stored in the cache database, the rows content are
converted to a JSON string. The return type of get_rows_response has
changed: it's a 4-tuple, with optional json_content_rows and
content_rows.

BREAKING CHANGE: 🧨 return type of get_rows_response has changed