test: replace leche helper function with native forEach

[lumirlumir]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

In this PR, I've replaced leche helper function with native forEach.

This PR was motivated by #78, since leche was the only blocker preventing the update of mocha. (leche was last updated 6 years ago and hasn't been updated since.)

https://github.com/eslint/eslint-release/actions/runs/18691775165/job/53299023443?pr=78

---

I've looked into the original implementation of leche.withData, and it was as follows:

	/**
	 * A data provider for use with Mocha. Use this around a call to it() to run
	 * the test over a series of data.
	 * @param {Object|Array} dataset The data to test.
	 * @param {Function} testFunction The function to call for each piece of data.
	 * @returns {void}
	 * @throws {Error} If dataset is missing or an empty array.
	 */
	withData: function(dataset, testFunction) {

		// check for missing or null argument
		if (typeof dataset !== 'object' || dataset === null) {
			throw new Error('First argument must be an object or non-empty array.');
		}

		/*
		 * The dataset needs to be normalized so it looks like:
		 * {
		 *      "name1": [ "data1", "data2" ],
		 *      "name2": [ "data3", "data4" ],
		 * }
		 */
		var namedDataset = dataset;
		if (dataset instanceof Array) {

			// arrays must have at least one item
			if (dataset.length) {
				namedDataset = createNamedDataset(dataset);
			} else {
				throw new Error('First argument must be an object or non-empty array.');
			}
		}

		/*
		 * For each name, create a new describe() block containing the name.
		 * This causes the dataset info to be output into the console, making
		 * it easier to determine which dataset caused a problem when there's an
		 * error.
		 */
		for (var name in namedDataset) {
			if (namedDataset.hasOwnProperty(name)) {
				/*eslint-disable no-loop-func*/

				describe('with ' + name, (function(dataName) {
					return function() {

						var args = namedDataset[dataName];

						if (!(args instanceof Array)) {
							args = [args];
						}

						testFunction.apply(this, args);
					};
				}(name)));

				/*eslint-enable no-loop-func*/
			}
		}
	}

I thought it would be safe to replace the above function with forEach, so I went ahead.

What changes did you make? (Give an overview)

In this PR, I've replaced leche helper function with native forEach.

Related Issues

N/A

Is there anything you'd like reviewers to focus on?

N/A