Refactor CI workflow and update Cargo.toml; add main.rs for IoT paylo…

[Alhaji-naira]

Overview

This PR resolves multiple infrastructure, developer experience (DX), and audit preparation issues to ensure the codebase is secure, optimized, and strictly tested.

Changes Made

• CI/CD Pipeline: Added a new GitHub Actions workflow (.github/workflows/ci.yml) that automatically runs code formatting, clippy linting, unit tests, and compiles the .wasm artifact on every PR and push to main.
• WASM Optimization: Documented and verified the Cargo.toml release profiles (opt-level = "z", lto = true, strip = "symbols") to significantly reduce the compiled contract size and minimize deployment gas costs.
• IoT Testing Tool: Built a local Rust CLI tool (tools/iot-payload-generator) that securely generates valid ed25519 key pairs, mock hardware signatures, and JSON payloads for fast local testnet injection.
• Audit Documentation: Standardized inline codebase comments across contracts/utility_contracts/src/lib.rs. All core public API functions now have enterprise-grade /// doc-comments detailing inputs, returns, and panics to prepare for the upcoming Zealynx security audit.

Closes #207
Closes #208
Closes #209
Closes #210

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