Reimplemented space handling by introducing an address_space structure.

- Fixed potential concurrency bugs due to preemption being enabled.
- Introduced a new address space structure to better account for
  address spaces and page tables.
- Currently executes fine up to forking. Will investigate.

src/api/space.c

@@ -29,7 +29,7 @@ int sys_map(syscall_context_t *regs)
 		target = current;
 		goto found;
 	} else 	/* else search the tcb from its hash list */
-		if ((target = find_task(tid)))
+		if ((target = tcb_find(tid)))
 			goto found;
 
 	BUG();
@@ -56,7 +56,7 @@ int sys_unmap(syscall_context_t *regs)
 
 	if (tid == current->tid)
 		target = current;
-	else if (!(target = find_task(tid)))
+	else if (!(target = tcb_find(tid)))
 		return -ESRCH;
 
 	for (int i = 0; i < npages; i++) {