Fix circular dependency detection and self-dependency check

[shellicar]

Summary

• Add circular dependency detection that throws CircularDependencyError instead of silently stack overflowing
• Fix self-dependency check that was unreachable due to comparing abstract class against concrete class
• Add CircularDependencyError exported error class
• Add 7 tests covering self-dependency, 2-node cycles, and 3-node cycles across all lifetimes

Co-Authored-By: Claude noreply@anthropic.com