refactor!: remove art-template support

[Fdawgs]

closes #463. Breaking change.

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

Pull Request Overview

This PR removes art-template support as part of a refactor that introduces a breaking change. Key changes include:

• Removing art-template from the list of supported engines in index.js.
• Deleting the art-template rendering function and its related configuration.
• Updating documentation and benchmark files to eliminate art-template references.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

File	Description
index.js	Removed art-template from supported engines, its rendering function, and associated config.
README.md	Removed art-template documentation from the list of supported engines and examples.
benchmark/fastify-art.js	Deleted the benchmark file targeting art-template support.

Comments suppressed due to low confidence (2)

index.js:391

• Ensure that removal of art-template support is fully reflected in the test suite to avoid accidental references to a non-existent engine.

async function viewArtTemplate (page, data) {

benchmark/fastify-art.js:1

• Confirm that any benchmark tests for art-template have been removed or updated to prevent failures due to the removed engine support.

'use strict'

[simoneb]

LGTM, thanks for this 👌

[Fdawgs]

Cheers @simoneb, just want one more review, considering this is a breaking, then i'll merge and do a release.

[mcollina]

lgtm

[gurgunday]

Approved!