Spacetime Substantivalism 37: The Physical Essence of Light-like, Time-like, and Space-like Intervals as Validated by Multi-Messenger Astronomy — Also on the Ontological Reduction of the Null Geodesic Condition (ds²=0), the Deconstruction of Local Light Cones, the Weak Equivalence Principle, and the Substantive Genesis of Kinetic Energy and Momentum | Synapse