extents: add types

* lint code

boxes/extents.py

@@ -1,19 +1,19 @@
 class Extents:
     __slots__ = "xmin ymin xmax ymax".split()
 
-    def __init__(self,xmin=float('inf'),ymin=float('inf'),xmax=float('-inf'),ymax=float('-inf')) -> None:
+    def __init__(self, xmin: float = float('inf'), ymin: float = float('inf'), xmax: float = float('-inf'), ymax: float = float('-inf')) -> None:
         self.xmin = xmin
         self.ymin = ymin
         self.xmax = xmax
         self.ymax = ymax
 
-    def add(self,x,y):
+    def add(self, x: float, y: float) -> None:
         self.xmin = min(self.xmin, x)
         self.xmax = max(self.xmax, x)
         self.ymin = min(self.ymin, y)
         self.ymax = max(self.ymax, y)
 
-    def extend(self,l):
+    def extend(self, l) -> None:
         for x, y in l:
             self.add(x, y)