[TESTING] Add inline and related object operation tests

[7tg]

Description

Missing test coverage for complex inline operations and related object handling.

Missing Inline Tests

• test_inline_custom_form_validation_errors - Invalid data in inline form
• test_inline_multiple_fk_to_parent_uses_fk_name - Multiple FKs to same parent
• test_inline_ambiguous_parent_fk - Inline without explicit parent FK
• test_inline_create_missing_parent_fk - Missing parent_id in data
• test_inline_extra_fields_handling - Extra fields outside model
• test_inline_delete_with_cascade - Delete inline with children
• test_inline_permission_check_per_operation - Different permissions for create/update/delete

Missing Related Object Tests

• test_related_empty_reverse_accessor - Reverse relation with no items
• test_related_fk_target_deleted - FK target deleted after creation
• test_related_m2m_with_through_model - Complex M2M relationships
• test_related_with_custom_manager_queryset - Custom get_queryset()
• test_related_m2m_pagination - Offset/limit on M2M relations

Missing Bulk Tests

• test_bulk_create_all_same_fk_parent - Batch FK assignment
• test_bulk_update_different_fields_per_item - Partial field updates
• test_bulk_with_readonly_fields - Readonly fields in bulk format
• test_bulk_delete_with_cascade_effects - Cascade behavior

Example Test

@pytest.mark.django_db
@pytest.mark.asyncio
async def test_inline_permission_check(author, token_change_author_only, async_client):
    """Verify inline create requires add permission on inline model."""
    response = await async_client.post(
        "/mcp/",
        json={
            "method": "tools/call",
            "params": {
                "name": "update_author",
                "arguments": {
                    "id": author.id,
                    "data": {"name": "Updated"},
                    "inlines": {
                        "articles": [
                            {"title": "New Article", "content": "..."}
                        ]
                    }
                }
            }
        },
        headers={"Authorization": f"Bearer {token_change_author_only.token}"}
    )
    data = response.json()
    # Should fail because token doesn't have add_article permission
    assert "permission_denied" in str(data) or "error" in data