Optimize library with ESP8266/ESP32 support and more robust serial handling

[99buntai]

Overview

This PR provides a major update (v2.0.0) to the DFRobotDFPlayerMini library with significant improvements in reliability and cross-platform support.

Key Improvements

• Added robust support for ESP8266 and ESP32 platforms
• Implemented non-blocking serial communication with proper timeout handling
• Added state machine for packet parsing to prevent buffer overflows
• Improved watchdog timer compatibility for ESP boards
• Added optional debug logging capability
• Maintained full API compatibility with the original library

Technical Details

• Rewrote serial communication handling with proper frame validation
• Implemented safe, non-blocking waits with timeouts
• Added thread-safe design for multiple instances
• Improved error handling and recovery
• Added comprehensive serial protocol documentation

Documentation Updates

• Added detailed serial protocol documentation in markdown format
• Created CHANGELOG.md for version tracking
• Added GitHub Actions workflow for automated testing
• Updated README with new features and improvements
• Added proper MIT license attribution

Testing

• Tested on Arduino (AVR), ESP8266, and ESP32 platforms
• Verified backward compatibility with existing sketches
• Confirmed proper handling of long-running operations
• Validated watchdog timer compatibility

Breaking Changes

None. This update maintains full API compatibility with the original library while adding new capabilities.

Version

Bumped to version 2.0.0 due to significant internal improvements.