BSE: refactor screened potential
- Add dataclass with screened potential
- Remove wfile (saving) functionality for now, since it adds complicated (and buggy) code paths
- Simplify apparent spaghetti into some cached properties, up to and including the entire screened potential. Apparently it does not need to change in response to any variables, so it can be a cached property without compromising correctness. Or so I'd like to think.
Edited by Ask Hjorth Larsen