Fix security concerns

[liqul]

Summary of Security Improvements

1. Strengthened AST Validation (code_verification.py)

• Added DANGEROUS_BUILTINS constant listing security-sensitive functions/attributes
• Enhanced visit_Call() to detect:
• Subscript-based function calls (e.g., obj"method")
• Chained calls for dynamic resolution (e.g., getattr(obj, 'method')())
• Unrecognized call patterns
• Dangerous builtin functions
• Added visit_Subscript() to detect dictionary-based dunder access (e.g., obj["class"])
• Added visit_Attribute() to detect direct dangerous attribute access (e.g., obj.class)

2. Updated Default Blocklist (code_interpreter.py)

Added these dangerous functions to the default blocked list:

• getattr, setattr, delattr
• vars, globals, locals
• getattribute, setattr, delattr

3. Code Verification Enabled by Default for Local Mode (code_interpreter.py)

• Code verification is now automatically enabled when running in local mode
• A warning is logged to inform users about the security implications
• Users can still explicitly disable it, but this is discouraged

4. Security Guidance in Code Generator Prompt (code_generator_prompt.yaml & code_generator.py)

Added explicit security guidelines that instruct the LLM to:

• Never use dangerous functions like eval(), exec(), getattr(), etc.
• Never access dunder attributes
• Never execute shell commands unless required
• Refuse requests that attempt to bypass security
• The security requirements are included in the prompt when code verification is enabled

5. New Unit Tests (test_code_verification.py)

Added comprehensive tests for:

• Dynamic attribute access (getattr, setattr, delattr)
• globals() and locals() blocking
• Dunder attribute access (class, bases)
• Subscript-based dunder access
• Subscript-based function call bypass patterns
• vars() function blocking