[CLEAN] Synthetic Benchmark PR #30552 - feat(graph-engine): make layer runtime state non-null and bound early

[bar-qodo]

Benchmark PR langgenius#30552

Type: Clean (correct implementation)

Original PR Title: feat(graph-engine): make layer runtime state non-null and bound early
Original PR Description: > [!IMPORTANT]

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Summary

Fixes langgenius#30551.

• Introduce an uninitialized read-only runtime state and explicit error to keep GraphEngineLayer.graph_runtime_state non-null while surfacing early access.
• Bind layer runtime context when registering layers and align built-in layers with the new contract.
• Update docs and tests around layer initialization, and remove a truthiness guard that now raises under the new sentinel.

Screenshots

Before	After
N/A	N/A

Checklist

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

Original PR URL: langgenius#30552