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/server/server.c

@@ -1,108 +1,20 @@
 #include "chunk.h"
+#include "compression.h"
 #include "config.h"
 #include "data.h"
 #include "file.h"
+#include "io.h"
 #include "log.h"
+#include "metadata.h"
 #include "multiprocessing.h"
+#include "protocol.h"
 #include "queue.h"
-#include "socket.h"
+#include "transport_tcp.h"
 #include "unistd.h"
 #include "utils.h"
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <threads.h>
-
-File *file_receive(Config *config, int file_descriptor) {
-  char *path = (char *)receive_str(file_descriptor);
-  File *file = file_create(path);
-  free(path);
-  if (config->use_metadata)
-    file->metadata = file_receive_metadata(file_descriptor);
-  Data *file_data = receive_data(file_descriptor);
-  if (config->use_compression) {
-    Data *file_data_uncompressed = data_decompress(file_data);
-    data_destroy(file_data);
-    file_data = file_data_uncompressed;
-  }
-  data_destroy(file->data);
-  file->data = file_data;
-  return file;
-}
-
-static void receive_chunk_enqueue(int file_descriptor,
-                                  PipelineContextReceiver *context) {
-  Data *chunk_data = receive_data(file_descriptor);
-  Data *data_to_process = chunk_data;
-  if (context->config->use_compression) {
-    data_to_process = data_decompress(chunk_data);
-    data_destroy(chunk_data);
-  }
-  Chunk *chunk = chunk_deserialize(data_to_process, context->config->use_metadata);
-  data_destroy(data_to_process);
-
-  for (int i = 0; i < chunk->element_count; i++) {
-    File *file = chunk->items[i];
-    chunk->items[i] = NULL;
-    queue_enqueue_multithreaded(context->queue, file, &context->mutex,
-                                &context->condition_not_empty,
-                                &context->condition_not_full);
-  }
-  chunk_destroy(chunk);
-}
-
-int receive_thread(void *pipeline_context) {
-  PipelineContextReceiver *context =
-      (PipelineContextReceiver *)pipeline_context;
-  mtx_lock(&context->mutex);
-  int file_descriptor = context->file_descriptor;
-  Config *config = context->config;
-  mtx_unlock(&context->mutex);
-
-  Status status = receive_status(file_descriptor);
-  while (status == STATUS_NEXT || status == STATUS_CHUNK) {
-    if (status == STATUS_CHUNK) {
-      receive_chunk_enqueue(file_descriptor, context);
-    } else {
-      File *file = file_receive(config, file_descriptor);
-      queue_enqueue_multithreaded(context->queue, file, &context->mutex,
-                                  &context->condition_not_empty,
-                                  &context->condition_not_full);
-    }
-    status = receive_status(file_descriptor);
-  }
-  mtx_lock(&context->mutex);
-  context->receiver_done = true;
-  cnd_signal(&context->condition_not_empty);
-  mtx_unlock(&context->mutex);
-  return thrd_success;
-}
-
-int write_thread(void *pipeline_context) {
-  PipelineContextReceiver *context =
-      (PipelineContextReceiver *)pipeline_context;
-  mtx_lock(&context->mutex);
-  bool save_to_disk = context->config->save_to_disk;
-  char *root_directory = str_dup(context->config->receive_root_directory);
-  mtx_unlock(&context->mutex);
-
-  while (true) {
-    File *file = queue_dequeue_multithreaded(
-        context->queue, &context->mutex, &context->condition_not_empty,
-        &context->condition_not_full, &context->receiver_done);
-    if (file == NULL) {
-      free(root_directory);
-      return thrd_success;
-    }
-    if (save_to_disk) {
-      char *disk_path = path_cat(root_directory, file->path);
-      to_disk(disk_path, file->data->data, file->data->size);
-      file_restore_metadata(disk_path, file->metadata);
-      free(disk_path);
-    }
-    file_destroy(file);
-  }
-}
 
 int receive_files(Config *config, int file_descriptor) {
   Status status = receive_status(file_descriptor);