Add Eulerian path/circuit analyzer with Hierholzer's algorithm, edge connectivity, Chinese Postman suggestions, and report generation

EulerianPathAnalyzer — detects Eulerian circuits and paths via degree analysis,
finds actual paths using Hierholzer's O(V+E) algorithm, computes edge connectivity
via max-flow, suggests edge additions for non-Eulerian graphs (Chinese Postman
lower bound), generates human-readable reports. Handles edge cases: empty graphs,
isolated vertices, disconnected components. 38 tests.

Author: sauravbhattacharya001