feat(chvt): use custom implementation instead of system()

Calling system() is vulnerable and shouldn't be used.

include/chvt.h

@@ -0,0 +1,21 @@
+#ifndef _CHVTH_
+#define _CHVTH_
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+#define KDGKBTYPE 0x4b33
+#define VT_ACTIVATE 0x5606
+#define VT_WAITACTIVE 0x5607
+
+/**
+ * @brief change foreground virtual terminal to `n`
+ *
+ * @param n virtual terminal number
+ * @return int non-negative value on success
+ */
+int chvt(int n);
+
+#endif