return immutable static constant when calling #zero in Vector3i and Vector3f

[ieatglu3]

Vector3f and Vector3i both returned a new vector object when calling the zero() method; this is unnecessary as Vector3f and Vector3i components are immutable. I considered it may have been intentional, although I see in the Vector3d class, that this isn't the case, and its zero() method does indeed return a static constant

packetevents/api/src/main/java/com/github/retrooper/packetevents/util/Vector3d.java

Line 289 in bbeec89

return ZERO;

So it may have just been forgotten to be implemented in its float and integer counterparts.