Migrate from mocha to Node.js native test runner

Includes coverage reports when using Node.js 22 onwards

test/unit/toFormat.js

@@ -1,6 +1,7 @@
 // Copyright 2013 Lovell Fuller and others.
 // SPDX-License-Identifier: Apache-2.0
 
+const { describe, it } = require('node:test');
 const assert = require('node:assert');
 const sharp = require('../../');
 const fixtures = require('../fixtures');