Structure Configurator

Adds structure search, spacing, and safety configs to control where structures can be placed, their spacing from each other, and protects the server against crashing from jigsaw errors and random-source errors.

Details

• Configures structure search radii for worldgen, maps, and locate commands.
• Configures random-spread spacing and separation.
• Warns instead of crashing on some missing registry entries.
• Guards legacy random-source crashes and bad jigsaw final states.
• Adds structure diagnostics commands.
• Keeps the structureconfigurator mod id for compatibility.