fix(sockets): improve socket connection reliability and callback cleanup

[ImDevinC]

Summary

This PR fixes critical issues with Discord socket connection handling and callback management that were causing connection failures and potential memory leaks.

Changes

Socket Connection Improvements:

• Replace non-blocking socket operations with proper timeout-based approach
• Add socket connection timeout (2s) for better error handling
• Replace select() polling with socket.settimeout() for cleaner code
• Use sendall() instead of manual chunked sending for reliability
• Add SOCKET_BAD_BUFFER_SIZE error code to distinguish buffer issues from disconnects
• Improve error handling during initial handshake phase

Callback Registration & Cleanup:

• Register callbacks with both backend and plugin_base to prevent leaks
• Implement clear_callbacks() method in main plugin class
• Ensure callbacks are properly removed from both locations during cleanup
• Add proper callback tracking in DiscordCore for lifecycle management

Technical Details

Socket Changes (discordrpc/sockets.py):

• Connection now uses SOCK_STREAM explicitly with 2s timeout
• Send operations use sendall() with 5s timeout
• Receive operations use direct timeout (5s) instead of select()
• Better buffer size validation with dedicated error code

Callback Changes (actions/DiscordCore.py, main.py):

• Callbacks registered with plugin_base.add_callback() for global tracking
• Cleanup calls plugin_base.remove_callback() to prevent orphaned callbacks
• New clear_callbacks() method handles safe callback removal

Testing

These changes fix:

• Socket connection timeouts and hangs
• Race conditions in callback registration
• Memory leaks from unreleased callbacks
• Buffer size validation errors

Related

Builds on the performance improvements from PR #61