Levelburst - first release

• Level-up celebrations: expanding ground rings, a rising spiral of end rod sparks and a floating level title.
• Milestone celebrations with a sweeping light pillar made of block displays, colored beams, a glow outline and firework-style particle bursts.
• Default milestones at levels 10, 30 and 50; level 50 also announces to the whole server.
• Per-player toggle: /levelburst toggle, on, off.
• Admin tools: /levelburst preview (at a player or at coordinates) and /levelburst reload.
• Config options for view radius, active celebration cap, minimum level, disabled worlds and full styling of every celebration.
• Supports Paper 1.21 - 1.21.11 and 26.1.1 - 26.3.