test: add comprehensive unit tests for SDK enhancements

Create extensive unit test suites for all new features:

- WebRTCStatsMonitor: Tests for network quality monitoring, stats collection,
  quality assessment, issue detection, and lifecycle management
- DevicePreferenceManager: Tests for device recovery strategies, preference
  management, smart fallback logic, and error handling
- CallRecoveryManager: Tests for recovery orchestration, trigger handling,
  attempt tracking, and integration with network monitoring
- VisibilityManager: Tests for page visibility detection, optimization
  coordination, timeout handling, and browser compatibility
- UserExperienceManager: Tests for unified interface, video element management,
  fullscreen coordination, and configuration updates

Tests cover initialization, core functionality, error handling, edge cases,
configuration updates, event handling, state management, and cleanup.

Demonstrates comprehensive testing approach with proper mocking, async handling,
and integration patterns for complex SDK features.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: mjerris