ArbSphere - Federated Cross-Exchange Equity Arbitrage Primitives (Toy MVP)

Overview
- Provides a minimal, test-driven prototype of canonical ArbSphere primitives:
  - LocalArbProblem, SharedSignals, PlanDelta, DualVariables, AuditLog, PrivacyBudget
- A lightweight EnergiBridge-like IR mapping (arbsphere.ir.map_to_ir)
- A tiny ADMM-style coordinator (arbsphere.coordinator.admm_lite_step)
- A Graph-of-Contracts registry scaffold (arbsphere.go_registry.GoCRegistry)
- Toy adapters (price feed, broker) to bootstrap interoperability

How to run tests
- Ensure Python 3.8+ is available
- Run: pytest -q
- (Optional) Run packaging check: python -m build

Notes
- This is a production-oriented scaffold focused on deterministic replay, auditable provenance, and interoperability. It is not a complete trading system.