[refurb] Make example error out-of-the-box (FURB157)

[MeGaGiGaGon]

Summary

Part of #18972

This PR makes verbose-decimal-constructor (FURB157)'s example error out-of-the-box.

Old example

Decimal("0")
Decimal(float("Infinity"))

New example

from decimal import Decimal

Decimal("0")
Decimal(float("Infinity"))

Imports were also added to the "Use Instead" section.

Test Plan

N/A, no functionality/tests affected

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.