[Feature]: Added SIGHUP handling

[douxxtech]

Now when nasmserver gets a signal 1 (SIGHUP), the config path is automatically reloaded with the newer values.

Some elements can't be hot-reloaded, such as the document root, bind address/port, log file path, and chroot/privilege-drop settings. These still require a full restart to take effect.

[github-actions]

START + GET /: 168 syscalls
Fastest: 0.000015s (clock_gettime)
Slowest: 0.894162s (accept)

threads: 4 (auto), conns: 50, duration: 20s

[wrk]
Running 20s test @ http://127.0.0.1:8080/
  4 threads and 50 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency     4.96ms    9.59ms 418.32ms   99.52%
    Req/Sec     1.65k   350.91     2.73k    69.00%
  131971 requests in 20.05s, 200.24MB read
  Socket errors: connect 0, read 770, write 0, timeout 0
Requests/sec:   6583.02
Transfer/sec:      9.99MB