[Lint]Style: Convert example to ruff format (#5863)

### What this PR does / why we need it?
This PR fixes linting issues in the `example/` to align with the
project's Ruff configuration.

- vLLM version: v0.13.0
- vLLM main:
bde38c11df

Signed-off-by: root <root@LAPTOP-VQKDDVMG.localdomain>
Co-authored-by: root <root@LAPTOP-VQKDDVMG.localdomain>

.pre-commit-config.yaml

@@ -4,7 +4,6 @@ default_install_hook_types:
 default_stages:
   - pre-commit # Run locally
   - manual # Run in CI
-exclude: 'examples/.*' # Exclude examples from all hooks by default
 repos:
 - repo: https://github.com/astral-sh/ruff-pre-commit
   rev: v0.14.0