## Summary

Add end-to-end relationship tests that validate the full relationship
API lifecycle against a live Dataverse environment. This is the primary
pre-GA validation for Tim's relationship PRs (#88, #105, #114).

## Changes

### New: `tests/e2e/test_relationships_e2e.py`
11 curated e2e tests covering:

| Test Class | Tests | Coverage |
|---|---|---|
| `TestOneToManyCore` | 1 | Full 1:N lifecycle: create, get, delete,
field assertions |
| `TestLookupField` | 1 | Convenience `create_lookup_field` to system
table |
| `TestManyToMany` | 2 | N:N lifecycle + nonexistent returns None |
| `TestDataThroughRelationships` | 4 | `@odata.bind`, `$expand`,
`$filter` on lookup, update binding |
| `TestCascadeBehaviors` | 2 | Restrict blocks delete; Cascade deletes
children |
| `TestTypeDetection` | 1 | `get_relationship` distinguishes 1:N vs N:N
|

### Updated: `examples/basic/functional_testing.py`
- Added relationship testing section covering 1:N core API, convenience
API, N:N, get, and delete
- Added relationship imports and retry helpers

### Updated: `pyproject.toml`
- Added `[tool.pytest.ini_options]` with `testpaths = ["tests/unit"]`
- Default `pytest` runs only unit tests; e2e tests require explicit
invocation

## How to run e2e tests

```bash
# Set your Dataverse org URL
export DATAVERSE_URL=https://yourorg.crm.dynamics.com

# Run relationship e2e tests
pytest tests/e2e/ -v -s
```

The tests authenticate via `InteractiveBrowserCredential` and
create/delete temporary tables (prefixed `test_E2E*`).

## E2E Test Results (from `.scratch/` comprehensive suite)

Ran 30 tests against `https://aurorabapenv71aff.crm10.dynamics.com`:
- 25/30 passed on first run
- 5 failures were test bugs (not SDK bugs), all fixed:
  - Metadata propagation timing (increased retries)
- Navigation property name casing (`$expand` needs server-assigned nav
prop)
- `IsValidForAdvancedFind` requires `BooleanManagedProperty` complex
type

## Finding: SDK inconsistency to address before GA

`create_one_to_many_relationship()` returns `lookup_schema_name` as the
user-provided SchemaName, but `$expand` requires the server-assigned
`ReferencingEntityNavigationPropertyName` (which may differ in casing).
The e2e tests work around this by calling `get_relationship()` after
create to get the correct nav prop name. This should be harmonized
before GA.

## Checklist

- [x] 398 unit tests pass
- [x] 11 e2e tests collected by pytest
- [x] Default `pytest` excludes e2e (runs unit only)
- [x] Code formatted with black
- [x] Branch rebased on origin/main

---------

Co-authored-by: Saurabh Badenkal <[email protected]>