Neo N3 Runtime facade

This crate provides a lightweight façade over the Neo runtime surface so integration tests and examples can exercise the canonical syscall catalogue without depending on a full node implementation. The implementation intentionally returns deterministic placeholder values – enough to validate wiring and type conversions while remaining self-contained for unit tests.

⚠️ Contract panic safety

In Neo N3, a runtime panic (panic!, unwrap() on None/Err, index out of bounds, arithmetic overflow) causes the VM to FAULT, which reverts the entire transaction. Unlike off-chain Rust, you cannot use panics for control flow in on-chain contracts. Always use NeoResult<T> and explicit error handling. The #[neo_contract] macro expects methods to return NeoResult<T> precisely because panics are unrecoverable on-chain.