feat: add contains functions

list.c

@@ -4,6 +4,7 @@
 
 #include "tstd/list.h"
 
+#include <stdint.h>
 #include <string.h>
 
 #include "helper.h"
@@ -64,4 +65,13 @@ void* list_delete_element(list* list, int index) {
         list->data[i] = list->data[i + 1];
     }
     return element;
-}
+}
+
+uint8_t list_contains(list* list, void* element) {
+    for (int i = 0; i < list->length; i++) {
+        if (list->data[i] == element) {
+            return 1;
+        }
+    }
+    return 0;
+}