Describe the bug
The WatutModFabric class contains a static reference to MinecraftServer in the form of public static MinecraftServer minecraftServer

This field is not set to null when the singleplayer integrated server is closed, causing the now-closed minecraftServer to leak.

To fix this memory leak, either:

• bind to ServerLifecycleEvents.SERVER_STOPPED and set minecraftServer to null
• replace the minecraftServer field with a WeakReference

To Reproduce
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latest.log, debug.log or crash report if the other 2 arent possible
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Expected behavior
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Screenshots
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Mod and Minecraft version:

• Version: MC 1.21.1, Watut 1.21.0-1.2.7

Additional context
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