sched: Implement basic scheduling and signal handling system

Note: this is probably 25% broken, but it works right now as written, so I hope it all works.

- Added a new scheduler header file (scheduler.h) defining task structures, scheduling policies, and signal handling mechanisms.
- Integrated scheduling functions into the syscall interface, including SYS_GETPID, SYS_GETPPID, SYS_EXIT, SYS_SCHED_YIELD, SYS_NICE, SYS_KILL, SYS_SIGACTION, SYS_SIGPROCMASK, SYS_SCHED_GETSCHEDULER, and SYS_SCHED_SETSCHEDULER.
- Updated syscall handler to manage new scheduling-related syscalls and signal actions.

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

user/programs/init.c

@@ -15,31 +15,31 @@ unsigned strlen(const char* str)
 
 void main()
 {
-    const char* path = "/qwerty.txt";
-    const char* msg  = "Suki Suki Daisuki Kekkon Shiyo, my honey!";
+    const unsigned char* path = "/qwerty.txt";
+    const unsigned char* msg  = "Suki Suki Daisuki Kekkon Shiyo, my honey!";
 
-    char buf[128];
+    unsigned char buf[128];
 
     // ── open file ─────────────────────────────
-    long fd = syscall(SYS_OPEN, (long)path, 0, 0);
+    unsigned long fd = syscall(SYS_OPEN, (long)path, 0, 0, 0, 0, 0);
 
     // ── write message ─────────────────────────
-    syscall(SYS_WRITE, fd, (long)msg, strlen(msg));
+    syscall(SYS_WRITE, fd, (long)msg, strlen(msg), 0, 0, 0);
 
     // ── close ────────────────────────────────
-    syscall(SYS_CLOSE, fd, 0, 0);
+    syscall(SYS_CLOSE, fd, 0, 0, 0, 0, 0);
 
     // ── reopen ───────────────────────────────
-    fd = syscall(SYS_OPEN, (long)path, 0, 0);
+    fd = syscall(SYS_OPEN, (long)path, 0, 0, 0, 0, 0);
 
     // ── read into buffer ─────────────────────
-    long n = syscall(SYS_READ, fd, (long)buf, sizeof(buf));
+    unsigned long n = syscall(SYS_READ, fd, (unsigned long)buf, sizeof(buf), 0, 0, 0);
 
     // ── close ────────────────────────────────
-    syscall(SYS_CLOSE, fd, 0, 0);
+    syscall(SYS_CLOSE, fd, 0, 0, 0, 0, 0);
 
     // ── print buffer to stdout ───────────────
-    syscall(SYS_WRITE, STDOUT, (long)buf, n);
+    syscall(SYS_WRITE, STDOUT, (unsigned long)buf, n, 0, 0, 0);
 
     // ── done ────────────────────────────────
     while (1);