[`refurb`] Make example error out-of-the-box (`FURB157`) (#19695)
## Summary
Part of #18972
This PR makes [verbose-decimal-constructor
(FURB157)](https://docs.astral.sh/ruff/rules/verbose-decimal-constructor/#verbose-decimal-constructor-furb157)'s
example error out-of-the-box.
[Old example](https://play.ruff.rs/0930015c-ad45-4490-800e-66ed057bfe34)
```py
Decimal("0")
Decimal(float("Infinity"))
```
[New example](https://play.ruff.rs/516e5992-322f-4203-afe7-46d8cad53368)
```py
from decimal import Decimal
Decimal("0")
Decimal(float("Infinity"))
```
Imports were also added to the "Use Instead" section.
