split(data/list/*): split off `data.list.basic` (#10164)
Killing the giants. This moves 700 lines off `data.list.basic` that were about
* `list.sum` and `list.product` into `data.list.big_operators`
* `list.countp` and `list.count` into `data.list.count`
* `list.sigma` and `list.prod` into `data.list.sigma_prod`
