refactor: optimize hash table iterations and fix security issues #58

- refactor(core): replace g_hash_table_get_keys with g_hash_table_iter_init
  * Eliminates temporary GList allocations
  * Improves iteration performance
  * Affected: connection.c, cmd_defs.c, cmd_funcs.c, omemo.c, gpg.c,
    disco.c, form.c, autocompleters.c, capabilities.c, callbacks.c

- fix(xmpp): correct queued_messages loop in connection.c:1031
  * Remove incorrect NULL check that prevented message storage
  * calloc zeros array, causing loop to skip immediately
  * Fixes dropped messages during reconnection with SM enabled

- fix(ui): prevent format string vulnerabilities in cons_show calls
  * Replace cons_show(variable) with cons_show("%s", variable)
  * Protects against format string attacks if variables contain %
  * Updated instances across cmd_funcs.c, connection.c, ox.c,
    console.c, core.c

src/xmpp/capabilities.c

@@ -171,16 +171,15 @@ caps_get_features(void)
 {
     GList* result = NULL;
 
-    GList* features_as_list = g_hash_table_get_keys(prof_features);
-    GList* curr = features_as_list;
-    while (curr) {
-        result = g_list_append(result, strdup(curr->data));
-        curr = g_list_next(curr);
+    GHashTableIter iter;
+    gpointer key, value;
+    g_hash_table_iter_init(&iter, prof_features);
+    while (g_hash_table_iter_next(&iter, &key, &value)) {
+        result = g_list_append(result, strdup((char*)key));
     }
-    g_list_free(features_as_list);
 
     GList* plugin_features = plugins_get_disco_features();
-    curr = plugin_features;
+    GList* curr = plugin_features;
     while (curr) {
         result = g_list_append(result, strdup(curr->data));
         curr = g_list_next(curr);