Sound::encode() position is no longer nullable

making this nullable was based on the invalid assumption that global sounds have no position, but it turns out they _do_ still use the position to make the sound come from the correct direction.

src/world/sound/EntityLandSound.php

@@ -44,7 +44,7 @@ class EntityLandSound implements Sound{
 		$this->blockLandedOn = $blockLandedOn;
 	}
 
-	public function encode(?Vector3 $pos) : array{
+	public function encode(Vector3 $pos) : array{
 		return [LevelSoundEventPacket::create(
 			LevelSoundEventPacket::SOUND_LAND,
 			$pos,