feat: extend tests & docs

[franklinkim]

Description

Extends test suite with graceful shutdown contract validation and goroutine leak detection; adds comprehensive Go documentation across all packages.

Type of Change

• 🐛 Bug fix
• ✨ New feature
• 💥 Breaking change
• 📝 Documentation
• ♻️ Refactoring
• 🏃‍➡️ Performance
• ✅ Tests
• 🔐 Security
• 🔧 Build/CI

Related Issues

Changes

• Add graceful shutdown contract tests to server_test.go
• Add goroutine leak detection checks via go.uber.org/goleak
• Generate Go package documentation (doc.go) across all modules and submodules
• Consolidate test setup utilities in helper_test.go

Checklist

• My code adheres to the coding and style guidelines of the project.
• I have performed a self-review of my own code.
• I have commented on my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.