add smart contract fuzzer

[Jim8y]

Neo Smart Contract Fuzzer Implementation

This PR implements a comprehensive fuzzing system for Neo N3 smart contracts. The fuzzer is designed to test Neo N3 smart contracts for various vulnerabilities and ensure they compile and run correctly.

Features

• Symbolic Execution Engine: Implements a symbolic execution engine that can analyze Neo smart contracts without actually running them
• Vulnerability Detection: Includes detectors for common smart contract vulnerabilities:
  • Reentrancy vulnerabilities
  • Integer overflow/underflow
  • Unauthorized access
  • Storage manipulation issues
  • Unsafe native contract calls
• Path Exploration: Explores multiple execution paths through a contract to find potential vulnerabilities
• Constraint Solving: Uses constraint solving to determine if vulnerability conditions can be satisfied

Implementation Details

• Uses the Neo.Compiler.CSharp CompilationEngine directly to compile contracts
• Generates proper NEF and manifest files for contract analysis
• Implements a symbolic virtual machine that can execute Neo VM instructions symbolically
• Provides detailed vulnerability reports with specific information about detected issues

Testing

• Comprehensive unit tests in Neo.SmartContract.Fuzzer.Tests verify the functionality of all components
• All 50 unit tests pass successfully

Future Work

• Expand vulnerability detection to cover more security issues
• Improve performance for analyzing complex contracts
• Add support for more advanced symbolic execution techniques
• Enhance reporting with more detailed vulnerability information and remediation suggestions

Documentation

Documentation for the Neo Smart Contract Fuzzer can be found in the docs/fuzzer/smartcontract directory.