WHAT: Implements continuation token pagination for the lookup_accessible_workspaces method in WorkspaceInventoryAccessChecker.

WHY: Previously, the implementation used a hardcoded INVENTORY_LIMIT of 10,000 workspaces. If a user had access to more than 10,000 workspaces, results would be silently truncated with only a warning log. This could cause users to not see all their accessible workspaces.