Add idp_attributes field to OrganizationMembership

- Add idp_attributes: dict[str, Any] to OrganizationMembership model
- Update MockOrganizationMembership fixture
- All organization_membership tests pass

This change adds support for IDP custom attributes on organization
memberships, which are sourced from the identity provider and stored
as customAttributes in the API.

Related to workos/workos PR #50470

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: ajworkos

src/workos/types/user_management/organization_membership.py

@@ -1,4 +1,4 @@
-from typing import Literal, Sequence, Optional
+from typing import Any, Literal, Sequence, Optional
 from typing_extensions import TypedDict
 
 from workos.types.workos_model import WorkOSModel
@@ -21,5 +21,6 @@ class OrganizationMembership(WorkOSModel):
     role: OrganizationMembershipRole
     roles: Optional[Sequence[OrganizationMembershipRole]] = None
     status: LiteralOrUntyped[OrganizationMembershipStatus]
+    idp_attributes: dict[str, Any]
     created_at: str
     updated_at: str

tests/utils/fixtures/mock_organization_membership.py

@@ -13,6 +13,7 @@ def __init__(self, id):
             organization_id="org_67890",
             status="active",
             role={"slug": "member"},
+            idp_attributes={},
             created_at=now,
             updated_at=now,
         )