Add multiplication operation (0:100*)

[Copilot]

Implements basic multiplication operation per request 0:100*.

Changes

• src/math.js: Export multiply(a, b) function
• test/math.test.js: Test coverage for edge cases (zero, negatives, range 0-100)
• package.json: Mocha test infrastructure

Usage

import { multiply } from './src/math.js';

multiply(50, 2);   // 100
multiply(0, 100);  // 0
multiply(-2, 3);   // -6

Original prompt

0:100*

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