## Changes
This PR adds comprehensive tests for `AshFeistelCipher.Transformer`.
### What's Added
- **Test Infrastructure**
- `test/support/repo.ex`: Test Ecto Repo
- `test/support/domain.ex`: Test Ash Domain
- `test/support/test_resources.ex`: Resource definitions for various
test scenarios
- **Comprehensive Test Coverage** (`test/transformer_test.exs`)
- Basic functionality tests
- Single encrypt configuration
- Multiple encrypt configurations
- Custom configuration tests
- Custom bits configuration
- Custom key configuration
- Custom functions_prefix configuration
- Custom PostgreSQL schema configuration
- Custom source attributes (DB column mapping)
- Edge case tests
- Duplicate target validation
- Down SQL generation
- Integration with FeistelCipher.Migration
### Test Results
✅ All 14 tests passing
### Dependency Updates
- `feistel_cipher` 0.7.0 → 0.7.1
## Checklist
- [x] Tests added
- [x] All tests passing
- [x] Dependencies updated