feat: add code complexity and maintainability analyzer

[upasana-2006]

Description

This PR adds a new Code Complexity & Maintainability Analyzer using Python's AST module.

Features Added

• Cyclomatic complexity calculation for Python functions
• Function-level complexity reporting
• Risk level classification (Low, Medium, High)
• Maintainability score generation
• Recommendations for highly complex code
• Unit tests covering simple functions, branching logic, loops, and invalid syntax

Benefits

• Helps developers identify refactoring opportunities
• Improves code quality insights provided by the platform
• Complements existing code analysis capabilities with maintainability-focused metrics

Related Issue

Fixes #445

Type of change

• Bug fix
• New feature / enhancement
• Documentation update
• Test addition
• Refactor

Checklist

• I have read CONTRIBUTING.md
• My branch is up to date with main
• I have run pytest -v and all tests pass
• I have not introduced duplicate issues or features
• My PR title follows the format: feat/fix/docs/test: short description
• I have added tests for new features (Level 2 and 3 issues)
• No hardcoded secrets or API keys in my code
• This PR is linked to a GSSoC 2026 issue

Screenshots (if frontend change)

N/A

Test evidence

pytest -v