Release v0.3.0

Overhaul cache system with key generation, async packaging, and thread safety

• Add flexible cache key generation with composable functions and metadata support
• Implement task ID to cache key mapping for reverse lookups
• Add automatic cleanup of stale mappings to prevent memory leaks
• Improve error handling during shutdown sequence
• Include comprehensive tests for new functionality
• Refactor cache module to package async_cache
• Fixed thread safety with dict locks in async_cache