fix: write correct entity y/z coordinates when saving clipboard to disk

[NyaNexNah]

Overview

Fixes a bug in DiskOptimizedClipboard where entity positions saved to a disk clipboard are corrupted. When writing entity NBT data, all three elements of the Pos list were set to the entity's x coordinate:

pos.add(new DoubleTag(entity.getLocation().x()));
pos.add(new DoubleTag(entity.getLocation().x())); // should be y
pos.add(new DoubleTag(entity.getLocation().x())); // should be z

The read side (loadNBTFromFileFooter()) correctly reads Pos[0..2] as x, y, z, so every entity loaded from a disk clipboard ends up with its y and z position replaced by x. This fixes the write side to use the y and z coordinates respectively.

Submitter Checklist

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