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/file.h

@@ -21,11 +21,8 @@ void file_load_data(File *file);
 void file_print(void *item);
 void file_send_single_calls(File *file, int file_descriptor);
 size_t file_content_to_buffer(File *file);
-Data *file_compress(File *file);
 
 FileReceive *file_receive_create(char *path, Data *data);
 void file_receive_destroy(void *file_receive);
-FileReceive *file_receive_from_buffer(void *buffer);
-FileReceive *file_receive_decompress(void *FileReceive);
 
 #endif