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/plugins/disco.c

@@ -107,10 +107,11 @@ disco_remove_features(const char* plugin_name)
         return;
     }
 
-    GList* plugin_feature_list = g_hash_table_get_keys(plugin_features_set);
-    GList* curr = plugin_feature_list;
-    while (curr) {
-        char* feature = curr->data;
+    GHashTableIter iter;
+    gpointer key, value;
+    g_hash_table_iter_init(&iter, plugin_features_set);
+    while (g_hash_table_iter_next(&iter, &key, &value)) {
+        char* feature = (char*)key;
         if (g_hash_table_contains(features, feature)) {
             void* refcountp = g_hash_table_lookup(features, feature);
             int refcount = GPOINTER_TO_INT(refcountp);
@@ -121,10 +122,7 @@ disco_remove_features(const char* plugin_name)
                 g_hash_table_replace(features, strdup(feature), GINT_TO_POINTER(refcount));
             }
         }
-
-        curr = g_list_next(curr);
     }
-    g_list_free(plugin_feature_list);
 }
 
 GList*