VFadeIn TypeError: len() of unsize object


### Error While Runing VFadeIn
here is the code,
```from manim_imports_ext import *

class Test(InteractiveScene):
def construct(self):
# Todo
sq = Square(side_length=0.5+MED_LARGE_BUFF)
sq.set_fill(BLUE_D, 0.7)
sq.set_stroke(BLUE_D, 5)
self.play(
DrawBorderThenFill(sq)
)
self.wait()
self.play(
sq.animate.shift(2*UP+2*RIGHT)
)

#new sq
sqs = VGroup(*(Square(side_length=0.5+MED_LARGE_BUFF) for n in range(3)))
sqs.arrange(RIGHT)
sqs.match_style(sq)
self.play(
LaggedStart(DrawBorderThenFill(sqs), lag_ratio=0.5)
)
self.play(LaggedStart(
sqs[1].animate.next_to(sq,RIGHT,buff=0),
sqs[0].animate.next_to(sq,UP,buff=0),
sqs[2].animate.next_to(sq,UR,buff=0),
),lag_ratio=0.4)

# VFadeIn
self.play(
FadeIn(DecimalNumber()),
run_time=2
)
# Why This Error? In VFadeIn??

The error occurs when calling VFadeIn on a DecimalNumber object. Look at the VFadeIn implementation in manim's animation files, likely in manim/animation/fading.py or similar. Check what VFadeIn expects as input and why DecimalNumber might be an 'unsize object'. Run the provided test scene to reproduce the TypeError and examine the stack trace. The fix may involve adjusting VFadeIn to handle objects without a defined length or ensuring DecimalNumber has the required attributes.

Written by the indexing model from the issue text.