refactor: extract receive_chunk_data and receive_manifest shared helpers

- receive_chunk_data(fd, config) -> Chunk*: shared receive/decompress/deserialize
  (eliminates ~25 lines of duplication between server.c and multiprocessing.c)
- receive_manifest(fd, config, next_status): moved from server.c to file.c,
  fixes missing 'Deleting files not in manifest...' log in multiprocessing.c
- Removes redundant manual free loop in multiprocessing.c manifest handling
  (array_list_create(free) destructor already handles this)
- server.c and multiprocessing.c: remove local chunk/manifest helpers,
  remove compression.h include (no longer needed)

src/shared/chunk.c

@@ -10,6 +10,7 @@
 #include "file.h"
 #include "log.h"
 #include "metadata.h"
+#include "protocol.h"
 
 Chunk *chunk_create(File **items, int element_count) {
   Chunk *chunk = (Chunk *)malloc(sizeof(Chunk));
@@ -178,5 +179,27 @@ Data *chunk_compress(Chunk *chunk, int compression_level, bool use_metadata) {
   return compressed;
 }
 
+Chunk *receive_chunk_data(int fd, Config *config) {
+  Data *chunk_data = receive_data(fd);
+  if (chunk_data == NULL) {
+    log_message(LOG_LEVEL_ERROR, "Failed to receive chunk data");
+    return NULL;
+  }
+  Data *data_to_process = chunk_data;
+  if (config->use_compression) {
+    data_to_process = data_decompress(chunk_data);
+    data_destroy(chunk_data);
+    if (data_to_process == NULL) {
+      log_message(LOG_LEVEL_ERROR, "Failed to decompress chunk");
+      return NULL;
+    }
+  }
+  Chunk *chunk = chunk_deserialize(data_to_process, config->use_metadata);
+  data_destroy(data_to_process);
+  if (chunk == NULL)
+    log_message(LOG_LEVEL_ERROR, "Failed to deserialize chunk, skipping");
+  return chunk;
+}
+