fix: skip listenHttpServer when using native Bun server

[cismuc]

Changes

• Added a check in _startServer to skip listenHttpServer when this.usingBunServer is active.

Why

When useBunServer is enabled, createBunServer calls Bun.serve(), which automatically starts listening on the configured host and port. Calling listenHttpServer afterwards attempted to register Node-style event handlers (server.on('error', ...)) on the Bun server instance, resulting in an unhandled TypeError: server.on is not a function at startup.

Checkmarks

• The modified endpoints have been tested.
• Used the same indentation as the rest of the project.
• Still compatible with LavaLink clients.
• Tested and verified locally, and in my deployment too

Additional information

• Updated compiled output in dist/src/index.js.

[github-actions]

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[cismuc]

I have read the CLA Document and I hereby sign the CLA