Clean up a small TODO in the store module

[Leomrlin]

What & why

The geaflow-store module has several small, well-scoped TODOs that make a great
doorway into the storage layer. For example,
geaflow-store-rocksdb/.../PartitionType.java has
// TODO: Support dt partition and // TODO: Support label dt partition, and
the API layer's OneDegreeGraphScanIterator has one too. Small scope, clear context.

geaflow-store 模块里有若干小 TODO,是读懂存储层的好切入点。比如
PartitionType.java 里的 // TODO: Support dt partition,以及 api 层
OneDegreeGraphScanIterator 的 TODO。范围小、上下文清晰。

The task

Claim one TODO and either implement it, or — if it's genuinely not ready to
implement — replace it with a clear validation + error message plus a doc note.
Prefer the ones that are well-scoped and testable.

认领其中一个 TODO,补全实现;或(若暂不宜实现)替换成清晰的校验与报错 + 文档说明。
优先选范围明确、能加测试验证的。

Where to look

1. Find the TODOs: grep -rn "TODO" geaflow/geaflow-plugins/geaflow-store/.
2. Mirror a similar, already-implemented branch in the same module.
3. Add a unit test covering the new path.

Done when

• The chosen TODO is implemented, or replaced by an explicit "not supported"
  check (throwing a clear exception rather than failing silently)
• A test covers the new behavior
• Existing store tests still pass (mvn test -pl <store-module>)
• The PR describes the scope of the change

[f0restron07]

hi @Leomrlin can u assign it to me i would like to work on it