fix: improve RADIUS client error handling and socket cleanup

[sharpenteeth]

Changes

This PR improves error handling and resource cleanup in the RADIUS client implementation.

Improvements

1. Enhanced error messages (server/util-server.js):

   • Preserves error stack traces for better debugging
   • Adds hostname and port context to error messages
   • Maintains original error information for troubleshooting

2. Fixed race conditions and memory leaks (server/radius-client.js):

   • Added proper socket cleanup function to prevent multiple cleanup calls
   • Introduced socketClosed flag to prevent operations on closed sockets
   • Improved timeout handling to ensure resources are properly released
   • Fixed potential race conditions between timeout callbacks and response handlers

Benefits

• Better error messages help identify RADIUS authentication issues faster
• Prevents potential memory leaks from improperly closed sockets
• Eliminates race conditions that could cause unexpected behavior
• More robust error handling improves overall reliability

Testing

These changes maintain backward compatibility and improve error handling without changing the API contract.

[github-actions]

Hello and thanks for lending a paw to Uptime Kuma! 🐻👋
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In particular: - Mark your PR as Draft while you’re still making changes - Mark it as Ready for review once it’s fully ready
If you have any design or process questions, feel free to ask them right here in this pull request - unclear documentation is a bug too.

[CommanderStorm]

Shure, thanks

[github-actions]

@dive2tech congrats on your first contribution to Uptime Kuma! 🐻
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