feat: Convert legacy verifiers to mellea reqlib

[0xCUB3]

Converts the imperative legacy verifiers into declarative mellea Requirements.

Precursor

The feat/llm-sandbox-execution branch that I already pushed to the main mellea repo provides the safe/unsafe execution structure with llm-sandbox.

Implementation

7 auto-fixing requirements:

• python_files_accessible - Creates missing data/image/text files automatically
• python_imports_resolved - Adds missing import statements with nickname support
• python_columns_accessible - Adds missing DataFrame columns with dummy data
• python_code_formatted - Fixes indentation and formatting with autopep8
• python_packages_installed - Auto-installs missing packages with correct mapping
• python_paths_fixed - Fixes file path issues (./ prefixes, missing data/)
• python_auto_fix - Iterative pipeline combining all fixes

Three utility modules support these requirements:

• data_generators.py - Random data generation for all data types
• file_utils.py - File type predicates / I/O operations
• metadata_utils.py - Directory structure conversion and reconstruction

API

# Mellea execution (re-exported)
from mellea_contribs.reqlib import python_executable, python_executable_sandbox, python_syntax_valid

# Auto-fixing requirements
from mellea_contribs.reqlib import (
    python_files_accessible, python_imports_resolved, python_columns_accessible,
    python_code_formatted, python_packages_installed, python_paths_fixed, python_auto_fix
)

# Usage
auto_req = python_auto_fix(max_iterations=5, use_sandbox=True)

Testing

• Added 18 tests
• Tested on ~50 Mellea-generated snippets of varying length and complexity