refactor: split monolithic modules and extract shared components

- Remove dead socket.c/socket.h (accumulated duplicate symbols)
- Extract compression.h/c (data_compress/decompress from data.c)
- Extract io.h/c (low-level I/O from protocol.c)
- Extract metadata.h/c (unified metadata wire format from file.c, chunk.c, utils.c)
- Split client.c into client_cli.c (CLI parsing) + client_send.c (send logic)
- Move receiver pipeline threads from server.c to multiprocessing.c
- Move to_disk/file_restore_metadata from utils.c to file.c/metadata.c
- Fix const qualifiers on to_disk and str_dup signatures
- Suppress chown unused-result warning

src/shared/utils.c

@@ -1,12 +1,9 @@
 #include "utils.h"
 #include "libgen.h"
-#include "sys/stat.h"
-#include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <time.h>
-#include <unistd.h>
+#include <sys/stat.h>
 
 void mkdir_r(char *path) {
   char *path_duplicate = malloc(strlen(path) + 1);
@@ -39,7 +36,7 @@ void mkdir_r(char *path) {
   free(path_current);
 }
 
-char *str_dup(char *string) {
+char *str_dup(const char *string) {
   if (string == NULL)
     return NULL;
   char *new_string = (char *)malloc(strlen(string) + 1);
@@ -47,34 +44,6 @@ char *str_dup(char *string) {
   return new_string;
 }
 
-void to_disk(char *path, void *data, unsigned long long data_size) {
-  char *directory = str_dup(path);
-  char *dir_to_free = directory;
-  directory = dirname(directory);
-  mkdir_r(directory);
-  FILE *file_pointer = fopen(path, "wb");
-  if (file_pointer == NULL) {
-    perror("Could not open File");
-    exit(EXIT_FAILURE);
-  }
-  fwrite(data, 1, data_size, file_pointer);
-  fclose(file_pointer);
-  free(dir_to_free);
-}
-
-void file_restore_metadata(const char *path, FileMetadata *metadata) {
-  if (metadata == NULL)
-    return;
-  chmod(path, metadata->mode & 07777);
-  chown(path, metadata->uid, metadata->gid);
-  struct timespec times[2];
-  times[0].tv_sec = 0;
-  times[0].tv_nsec = UTIME_OMIT;
-  times[1].tv_sec = metadata->mtime_sec;
-  times[1].tv_nsec = metadata->mtime_nsec;
-  utimensat(AT_FDCWD, path, times, 0);
-}
-
 char *path_cat(char *path1, char *path2) {
   if (path1 == NULL || *path1 == '\0')
     return str_dup(path2);