feat: implement chunk serialization protocol with -s flag

- Extract chunk_serialize/chunk_deserialize from chunk_compress/chunk_decompress
- Add STATUS_CHUNK to wire protocol for chunk-mode transfers
- Client: -s sends chunk via STATUS_CHUNK (serialized or compressed+serialized)
- Server: handle STATUS_CHUNK in both single-threaded and multithreaded paths
- Fix memory leak in receive_file_receive (free->data_destroy)
- Remove dead declarations: file_receive_from_buffer, file_receive_decompress,
  file_compress, chunk_data_to_disk, unused #defines

src/shared/chunk.h

@@ -6,8 +6,6 @@
 #include <sys/stat.h>
 
 #define DESIRED_CHUNK_SIZE 10 * 1024 * 1024
-#define FILE_PATH_SEPERATOR "#&&SEPP&&#"
-#define FILE_PATH_DATA_SEPERATOR "#&&SEPD&&#"
 
 typedef struct {
   File **items;
@@ -18,10 +16,11 @@ Chunk *chunk_create(File **items, int element_count);
 void chunk_destroy(void *chunk);
 void chunk_print(void *chunk);
 Data *chunk_format(Chunk *chunk);
+Data *chunk_serialize(Chunk *chunk);
+Chunk *chunk_deserialize(Data *data);
 Data *chunk_compress(Chunk *chunk, int compression_level);
 Chunk *chunk_decompress(Data *compressed_data);
 
 Data *chunk_data_create(void *data, unsigned long long data_size);
 void chunk_data_delete(void *chunk);
-void chunk_data_to_disk(Data *chunk, char *root_directory);
 #endif