Add bounds check in Remember to prevent potential bof panic

[chengpeng-wang]

Hi, I found the function Remember in the file sample/user.go does not check the lengths of the parameters keys and values. If the number of keys is greater than the one of values, the buffer access at line 103 would cause bof panic. This patch adds a length check in the Remember function to avoid this bof panic.

Although current test cases use matching lengths, adding this check improves robustness and makes the assumption explicit, which can help avoid unexpected panics if the function is reused elsewhere.

Let me know if you'd prefer returning an error instead of logging a fatal error—happy to adjust.