Add __slots__ entries.

[knotapun]

Hello, all this does is add a __slots__ entry to a few classes. this small change makes an outsized impact, reducing the size of instances dramatically, and leads the way to efficient and fully typed page extraction.

from pympler import asizeof
class Rect:
    def __init__(self, a, b, c, d):
        self.x0: float = float(a)
        self.y0: float = float(b)
        self.x1: float = float(c)
        self.y1: float = float(d)
class RectWSlot:
    __slots__ = ("x0", "y0", "x1", "y1")
    def __init__(self, a, b, c, d):
        self.x0: float = float(a)
        self.y0: float = float(b)
        self.x1: float = float(c)
        self.y1: float = float(d)
print(asizeof.asizeof(Rect(1, 2, 3, 4)))       # 624

print(asizeof.asizeof(RectWSlot(1, 2, 3, 4)))  # 160

[knotapun]

I noticed the reasoning for non-typed values on the Structure of Dictionary Outputs section.

If this pull gets merged, would you accept a pull that types the dictionaries?