Evaluate segments from the stored JSON

Migrate Core API flag evaluation logic onto `Segment.rules_data`.

### Acceptance criteria

- `SegmentRule` and `Condition` models are not used by engine and dynamo mappers.
- Identity segment evaluation (`Identity.get_segments`) returns the same matching segments before and after the change.
- `/api/v1/environment-document` serves rules from `Segment.rules_data`.
- The DynamoDB environment document contains identical segment data to the pre-change output.
- The project and environment segment caches feeding the mappers no longer issue rule or condition queries (assert query counts drop).