optimize VNC screen capture and improve keyboard handling

[vlad-terin]

I've made several optimizations to improve the screen capture performance:

1. Incremental Updates:

   • Added support for incremental updates by storing the last frame
   • Only sends changes since the last frame instead of the entire screen
   • This significantly reduces network traffic and processing time

2. Optimized Socket Reading:

   • Implemented a new _recv_exact method for efficient socket reading
   • Increased socket buffer size to 8192 bytes for better throughput
   • Uses buffered reading to reduce the number of socket calls

3. Image Processing Optimizations:

   • Added PNG compression optimization with quality=95
   • Reuses image objects when possible
   • Removed unnecessary error rectangles and debug logging

4. Error Handling Improvements:

   • Better error detection and handling
   • Early returns on critical failures
   • More informative error messages

You should notice:

• Faster initial screen capture
• Much faster subsequent captures (due to incremental updates)
• Lower CPU usage
• Reduced network traffic

[baryhuang]

I tested locally. It's working great! Thank you for the great improvement.

Feel free to merge any time.