Phase 1+2: bug fixes and dead code cleanup

Phase 1 — Bugs:
- receive_data: fix unsigned long long vs size_t mismatch
- chunk_deserialize: add NULL check in multiprocessing.c and server.c
- file_content_to_buffer: add missing fclose on error path
- send_files_multithreaded: propagate sender thread result
- server: add SIGPIPE handler
- to_disk: check fwrite return value
- scanner: use S_ISDIR instead of !S_ISREG
- scanner: free cur_path before early return

Phase 2 — Cleanup:
- Remove unused chunk_decompress function
- Remove unused array_list_clear function
- Remove unused num_connections config field
- Remove duplicate FILE_METADATA_WIRE_SIZE macro
- Update tests for removed APIs

src/shared/config.c

@@ -10,7 +10,7 @@ Config *config_create(char *version, char *send_directory,
                       char *receive_directory, bool save_to_disk,
                       bool use_multithreading, bool use_chunk_serialization,
                        bool use_compression, bool use_metadata,
-                       int compression_level, int num_connections, bool use_sendfile) {
+                       int compression_level, bool use_sendfile) {
 
   Config *config = malloc(sizeof(Config));
   config->version = version;
@@ -22,7 +22,6 @@ Config *config_create(char *version, char *send_directory,
   config->use_compression = use_compression;
   config->use_metadata = use_metadata;
   config->compression_level = compression_level;
-  config->num_connections = num_connections;
   config->use_sendfile = use_sendfile;
   config->transport = TRANSPORT_TCP;
   config->ssh_destination = NULL;
@@ -68,7 +67,6 @@ void config_send(int file_descriptor, Config *config) {
   send_int(file_descriptor, config->use_compression);
   send_int(file_descriptor, config->use_metadata);
   send_int(file_descriptor, config->compression_level);
-  send_int(file_descriptor, config->num_connections);
   send_int(file_descriptor, config->use_sendfile);
   if (receive_status(file_descriptor) != STATUS_OK) {
     perror("Error transmitting config!");
@@ -87,7 +85,6 @@ Config *config_receive(int file_descriptor) {
   config->use_compression = receive_int(file_descriptor);
   config->use_metadata = receive_int(file_descriptor);
   config->compression_level = receive_int(file_descriptor);
-  config->num_connections = receive_int(file_descriptor);
   config->use_sendfile = receive_int(file_descriptor);
   config->transport = TRANSPORT_TCP;
   config->ssh_destination = NULL;