Remove PJSIP Dependency

🚀 Major Changes

Remove PJSIP Dependency

This release removes the PJSIP C library dependency in favor of a pure Python asyncio implementation. This change
significantly simplifies installation and deployment.

Benefits:

• ✅ No external C library compilation required
• ✅ Easier installation: just uv sync - no build tools needed
• ✅ Better cross-platform compatibility
• ✅ Simplified development workflow
• ✅ Reduced system dependencies

Breaking Changes

⚠️ This is a breaking change

• PJSIP/PJSUA2 is no longer used. If you were relying on PJSIP-specific features, please
  review the new implementation.