fix: checkpoint store correctly initialize in multi-layered sub-workf…

[shentongmartin]

…low and workflow tool

What type of PR is this?

1. fix an issue when there are multi-layered sub-workflow and the root workflow requires checkpoint, inner nested sub-workflow won't initialize checkpoint store.
2. fix an issue when LLM node does not have workflow tool but still thinks it require checkpoint store.
3. fix an issue when workflow tool does not require checkpoint itself but its parent passed in checkpoint ID