Evolve transitive dep

[pranavkp71]

Description

This PR implements the First MVP of Transitive Dependency Analysis for DepWatch. It enables recursive scanning of nested dependencies via PyPI metadata, allowing users to see the full risk profile of their project's dependency tree.

Key Changes:

• Integrated a new PyPI JSON API client for resolving requires_dist.
• Implemented a BFS-based recursive resolver with cycle detection and depth limiting.
• Added --transitive / -t and --depth / -d flags to the CLI.
• Enhanced the CLI output to display dependency paths (e.g., fastapi → pydantic → pkg) and [direct] vs [transitive] labels.
• Updated the FastAPI backend to support transitive analysis in the /scan endpoint.
• Comprehensive unit tests added for the resolver logic.

Type of Change

• New feature
• Documentation update

Checklist

• Tests pass (pytest)
• Linting passes (ruff check .)
• Commit messages follow conventional format
• Documentation updated (if applicable)