fixup: address PR review comments

- Merge io.h/c back into protocol.h/c
- Change send_data to take Data* argument
- Remove redundant file_load_data from send_chunk
- Move compression into file_send_single_calls
- Move file_receive from multiprocessing.c to file.c

src/shared/protocol.h

@@ -2,15 +2,18 @@
 #define PROTOCOL_H
 
 #include "data.h"
-#include "io.h"
 #include <stddef.h>
 
 typedef int Status;
 enum NET_STATUS { STATUS_OK, STATUS_ERROR, STATUS_FINISHED, STATUS_NEXT, STATUS_CHUNK };
 
+void io_set_fds(int read_fd, int write_fd);
+void send_n_data(int file_descriptor, void *data, size_t data_size);
+void receive_n_data(int file_descriptor, void *data, size_t data_size);
+
 void send_str(int file_descriptor, char *data);
 char *receive_str(int file_descriptor);
-void send_data(int file_descriptor, void *data, unsigned long long data_size);
+void send_data(int file_descriptor, Data *data);
 Data *receive_data(int file_descriptor);
 void send_int(int file_descriptor, int data);
 int receive_int(int file_descriptor);