feat: added more lst functionality

srcs/lst/ft_lstinsert.c

@@ -0,0 +1,30 @@
+#include "libft.h"
+
+int ft_lstinsert(t_list **lst, t_list *node, int index)
+{
+    t_list *curr = *lst;
+    t_list *prev = NULL;
+    int i = 0;
+
+    if (index < 0 || !node)
+        return (-1);
+    if (index == 0)
+    {
+        node->next = *lst;
+        *lst = node;
+        return (0);
+    }
+    while (curr && i < index)
+    {
+        prev = curr;
+        curr = curr->next;
+        i++;
+    }
+    if (i == index)
+    {
+        prev->next = node;
+        node->next = curr;
+        return 0;
+    }
+    return (-1);
+}