Migrate from mocha to Node.js native test runner

Includes coverage reports when using Node.js 22 onwards

test/unit.mjs

@@ -0,0 +1,16 @@
+import { readdir } from 'node:fs/promises';
+import { run } from 'node:test';
+import { spec } from 'node:test/reporters';
+
+const files = (await readdir('./test/unit')).map((f) => `./test/unit/${f}`);
+
+run({
+  files,
+  concurrency: true,
+  timeout: 60000,
+  coverage: true,
+  coverageIncludeGlobs: ['lib/*.js'],
+  branchCoverage: 100,
+})
+  .compose(new spec())
+  .pipe(process.stdout);