Implementing Callback Functions in C

# Introduction

In this challenge, we will be working with callback functions in C language. Callback operations are common in Linux C program development, and function pointers are often used to implement them. The task is to debug and fix the bugs in the provided `callback.c` source file, so that the callback mechanism can execute properly and the output of the `demo.c` test program meets the expected output. Additionally, two exceptions need to be added to handle cases where the number of registered alarms exceeds the capacity of `alarm_list` and when there are no alarms registered for a given index in `alarm_list`. It is important to note that participants must not use alternate accounts to boost rankings and any abnormal behavior or cheating will be penalized.