[`refurb`] Make example error out-of-the-box (`FURB164`) (#19673)
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## Summary
<!-- What's the purpose of the change? What does it do, and why? -->
Part of #18972
This PR makes [unnecessary-from-float
(FURB164)](https://docs.astral.sh/ruff/rules/unnecessary-from-float/#unnecessary-from-float-furb164)'s
example error out-of-the-box.
[Old example](https://play.ruff.rs/807ef72f-9671-408d-87ab-8b8bad65b33f)
```py
Decimal.from_float(4.2)
Decimal.from_float(float("inf"))
Fraction.from_float(4.2)
Fraction.from_decimal(Decimal("4.2"))
```
[New example](https://play.ruff.rs/303680d1-8a68-4b6c-a5fd-d79c56eb0f88)
```py
from decimal import Decimal
from fractions import Fraction
Decimal.from_float(4.2)
Decimal.from_float(float("inf"))
Fraction.from_float(4.2)
Fraction.from_decimal(Decimal("4.2"))
```
The "Use instead" section also had imports added, and one of the fixed
examples was slightly wrong and needed modification.
## Test Plan
<!-- How was it tested? -->
N/A, no functionality/tests affected
