Adopt shared mapper test data from engine-test-data

Mapper tests use inline expected context data. When engine-test-data releases shared mapper test cases, this client should adopt them for cross-SDK consistency.

## Acceptance criteria
- [ ] Mapper test uses expected context from engine-test-data
- [ ] mapper_test_cases pass (see Flagsmith/engine-test-data#46)

## Technical context

Test data: https://github.com/Flagsmith/engine-test-data/pull/46

Start with the mapper tests and compare their inline expected context data with the shared mapper cases in engine-test-data PR #46. Done means the tests consume that shared expected context and mapper_test_cases pass.

Written by the indexing model from the issue text.