fix: fix a bug in the flow computation

The basic blocks flow graph algorithm has been
completely rewritten. It's now much more efficient, simpler
and fixes a bug which happens with -O4

Author: boriel

src/api/utils.py

@@ -6,7 +6,7 @@
 import shelve
 import signal
 from functools import wraps
-from typing import IO, Any, Callable, Iterable, List, Optional, Union, TypeVar
+from typing import IO, Any, Callable, Iterable, List, Optional, TypeVar, Union
 
 from src.api import constants, errmsg, global_