Final cleanup: fix imports and indentation

- Remove unused imports (array_map, count) from SubChunk.php
- Fix indentation in ChunkSerializer.php serializeSubChunk method
- Fix indentation in FastChunkSerializer.php serialize/deserialize methods
- Ensure consistent tab-based indentation throughout all modified files
- Clean up whitespace and formatting issues

src/network/mcpe/serializer/ChunkSerializer.php

@@ -112,7 +112,6 @@ final class ChunkSerializer{
 	}
 
 	public static function serializeSubChunk(SubChunk $subChunk, BlockTranslator $blockTranslator, PacketSerializer $stream, bool $persistentBlockStates) : void{
-		// Create array from non-empty layers
 		$layers = [];
 		if(!$subChunk->isBlockLayerEmpty()){
 			$layers[] = $subChunk->getBlockLayer();

src/world/format/SubChunk.php

@@ -23,9 +23,6 @@ declare(strict_types=1);
 
 namespace pocketmine\world\format;
 
-use function array_map;
-use function count;
-
 class SubChunk{
 	public const COORD_BIT_SIZE = 4;
 	public const COORD_MASK = ~(~0 << self::COORD_BIT_SIZE);