feat: add GraphEngine layer node execution hooks

[hieheihei]

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Summary

part of https://github.com/langgenius/dify/issues/28446

Extend the graph layer to inject OTel context

Screenshots

Checklist

• [ ] This change requires a documentation update, included: Dify Document
• [x] I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• [x] I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• [x] I've updated the documentation accordingly.
• [x] I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[fatelei]

python style check failed, you can

class Node:
      @property
      def execution_id(self) -> str:
          return self._node_execution_id

      def ensure_execution_id(self) -> str:
          if not self._node_execution_id:
              self._node_execution_id = str(uuid4())
          return self._node_execution_id

[fatelei]

add unittest:

Hook/event order: on_node_run_start -> NodeRunStartedEvent -> … -> NodeRunSucceeded/Failed -> on_node_run_end.

[hieheihei]

hi @fatelei This PR is ready for review, fixed Python style issues and adds unit tests for the Observability layer.

the "hook/event order" you mentioned: events appear to be handled asynchronously.But hooks are executed synchronously in the sequence on_node_run_start → node_execute → on_node_run_end. I believe this ordering is sufficient for the Observability layer.

[fatelei]

hi @fatelei This PR is ready for review, fixed Python style issues and adds unit tests for the Observability layer.

the "hook/event order" you mentioned: events appear to be handled asynchronously.But hooks are executed synchronously in the sequence on_node_run_start → node_execute → on_node_run_end. I believe this ordering is sufficient for the Observability layer.

ok

[fatelei]

git commit squash