Update to 1.21.3

[kermandev]

Fixes #22

Minestom

• Use new NetworkBuffer
• Template all serializers. (Way easier to add future debug draws)
• Create a small packet registry. (Write only)
• Deprecate NamespaceId for 1.21.4

Fabric

• Port mod to latest Fabric. This probably does not fix any issues with LineShape.Type.STRIP
• Delete existing mixins as they are no longer used and other mods do the same function as they once did.