[Test restructure 3] Move universal tests to universal directory

## What

- Move all cross-backend offline store tests from `integration/offline_store/` to `universal/offline_store/`.
- Move cross-backend online store tests from `integration/online_store/` to `universal/online_store/`.
- Move remaining universal tests to their new locations

## Files to move

| Source | Destination |
|--------|-------------|
| `integration/offline_store/test_universal_historical_retrieval.py` | `universal/offline_store/` |
| `integration/offline_store/test_universal_types.py` | `universal/offline_store/` |
| `integration/offline_store/test_universal_materialization.py` | `universal/offline_store/` |
| `integration/offline_store/test_offline_write.py` | `universal/offline_store/` |
| `integration/offline_store/test_non_entity_mode.py` | `universal/offline_store/` |
| `integration/offline_store/test_feature_logging.py` | `universal/offline_store/` |
| `integration/offline_store/test_persist.py` | `universal/offline_store/` |
| `integration/offline_store/test_push_features_to_offline_store.py` | `universal/offline_store/` |
| `integration/offline_store/test_dqm_validation.py` | `universal/offline_store/` |

**Stays in `integration/offline_store/`:**
- `test_s3_custom_endpoint.py` (needs S3, currently skipped)

| Source | Destination |
|--------|-------------|
| `integration/online_store/test_universal_online.py` | `universal/online_store/` |
| `integration/online_store/test_universal_online_types.py` | `universal/online_store/` |
| `integration/online_store/test_universal_e2e.py` | `universal/online_store/` |
| `integration/online_store/test_push_features_to_online_store.py` | `universal/online_store/` |

**Stays in `integration/`:**
- `test_remote_online_store.py` → move to `integration/auth/` (needs Keycloak)
- `test_hybrid_online_store.py` → move to `unit/` (fully mocked, no markers)

**`universal/registration/`:**
| Source | Destination |
|--------|-------------|
| `integration/registration/test_universal_registry.py` | `universal/registration/` |
| `integration/registration/test_universal_odfv_feature_inference.py` | `universal/registration/` |
| `integration/registration/test_feature_store.py` | `universal/registration/` |
| `integration/registration/test_inference.py` | `universal/registration/` |

**`universal/materialization/`:**
| Source | Destination |
|--------|-------------|
| `integration/materialization/test_universal_materialization.py` | `universal/materialization/` |

**Stays in `integration/materialization/`:**
- `test_lambda.py` (needs AWS)
- `test_snowflake.py` (needs Snowflake)
- `kubernetes/test_k8s.py` (needs EKS)

**`universal/cli/`:**
| Source | Destination |
|--------|-------------|
| `integration/cli/test_universal_cli.py` | `universal/cli/` |