Evaluate export partition scoping

[JayVDZ]

Summary

Evaluate whether and how partition-scoped export could be supported. This was identified as a future enhancement during #72 (Phase 3). This carries the most design complexity of the partition scoping work.

Key Challenges

• Requires PartitionId on CSOs (same prerequisite as Evaluate sync partition scoping #437) so pending exports can be routed to the correct partition.
• Cross-partition reference dependencies are a significant risk. Consider: users in Partition A, groups in Partition B. If an export is scoped to Partition B and JIM needs to both provision a new user in Partition A and add that user as a group member in Partition B, the membership export would fail — the referenced user doesn't exist yet because its partition wasn't included in the export.
• Solving this would require detecting cross-partition references in pending exports, building a dependency graph across partitions, and either pulling in dependent exports (defeating the purpose of scoping) or deferring/failing gracefully.
• Need to evaluate whether this complexity is justified and whether cross-partition references are common in real-world deployments.

Context

• Import partition scoping is already implemented and working (Confirm if a partition is needed/relevant for a Full Sync? #72 Phase 1)
• Sync partition scoping evaluation tracked in Evaluate sync partition scoping #437
• This is an evaluation task — the outcome may be "not worth the complexity"