Add design docs for resource hotspot detector, simulation adapter, cost comparison, and failure classifier

[bellabuks]

This PR adds design/spec docs for four related Soroban simulation & analysis features, following this repo's existing convention of design docs under docs/ (e.g. docs/soroban-cost-model-spec.md, docs/IMPLEMENTATION_SUMMARY.md).

Closes #813
Closes #814
Closes #815
Closes #816

• Implement Soroban Resource Hotspot Detector #813 — Design for a SorobanResourceHotspotDetector that ranks contract functions/source regions by normalized CPU/memory/ledger cost and surfaces them in the Soroban report.
• Implement Soroban Transaction Simulation Adapter #814 — Design for a SorobanSimulationAdapter package that builds, submits, and normalizes Soroban RPC simulateTransaction requests/responses.
• Implement Static-to-Simulation Cost Comparison #815 — Design for a StaticSimulationComparator that diffs static cost-model estimates against real simulation results and flags significant variance.
• Implement Soroban Simulation Failure Classifier #816 — Design for a SorobanSimulationFailureClassifier that categorizes raw RPC simulation errors into actionable, developer-facing explanations.

Docs added:

• docs/issue-813-resource-hotspot-detector.md
• docs/issue-814-transaction-simulation-adapter.md
• docs/issue-815-static-to-simulation-cost-comparison.md
• docs/issue-816-simulation-failure-classifier.md

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