feat(security): fix #329 by implementing missing circuit breaker detection rule

[TochukwuJustice]

closes #329
This pull request addresses issue #329 by introducing a new static analysis rule, MissingCircuitBreakerRule, within the GasGuard engine. Contracts lacking emergency stop mechanisms pose a significant security risk, as administrators cannot halt operations during an exploit. The new rule tokenizes the contract's AST and scans for common circuit breaker and pause-related keywords (e.g., pause, is_paused, Pausable, emergency, circuit_breaker). If the contract does not contain any recognizable pause logic, the engine flags it with a High severity violation, prompting developers to implement an emergency stop system to reduce incident severity.

4. Changes Made

• Added packages/rules/src/security/emergency/missing_circuit_breaker.rs implementing the circuit breaker detection logic and comprehensive test cases.
• Added packages/rules/src/security/emergency/mod.rs to expose the new rule module.
• Updated packages/rules/src/security/mod.rs to integrate the emergency module into the existing security rules registry.
• Addressed Detect Missing Circuit Breakers #329 by providing robust multi-pattern detection for missing pause mechanisms.

5. Testing

The rule was tested thoroughly via the GasGuard Rust test suite.
Command executed:

cd packages/rules && cargo test