OptionalcollisionOptionalcollisionAdditional group for the collision system only (default: none).
When set, the collision system belongs to both systemGroup and this group,
allowing independent enable/disable of collision detection.
OptionalgravityWorld gravity vector (default: {x: 0, y: 0})
OptionalintegrationPriority for integration system (default: 1000)
OptionalphaseExecution phase (default: 'fixedUpdate')
OptionalsystemSystem group name (default: 'physics2D')
Priority for collision system (default: 900)