Fix npm test on Node 24+

The test script passed --experimental-async-context-frame unconditionally.
Node 22/23 need it, but Node 24 turned AsyncContextFrame on by default and
removed the flag, so from Node 24 on `npm test` failed before running
anything:

    node: bad option: --experimental-async-context-frame

Replace it with a small runner in the style of build.js, which computes the
flag list from the running version. --disable-warning is conditional for the
same reason: it only exists from Node 21.3.

The computation lives in test/node-flags.js rather than inline in the runner
because tests that spawn a child need the same flag list.

npm test now runs on Node 22, 24 and 26; previously 24 and 26 could not run
it at all.

Author: szegedi

js/package.json

@@ -4,7 +4,7 @@
     "description": "Node.js writer for the OpenTelemetry thread-context record (OTEP-4947), discoverable via AsyncLocalStorage / AsyncContextFrame.",
     "main": "index.js",
     "scripts": {
-        "test": "node --experimental-async-context-frame --disable-warning=ExperimentalWarning --test test/test.js",
+        "test": "node test/run.js",
         "test:docker": "./test/run-in-docker.sh",
         "install": "node build.js"
     },

js/test/node-flags.js

@@ -0,0 +1,16 @@
+'use strict';
+
+// Node flags needed to make AsyncContextFrame — the writer's discovery
+// substrate — available on the running Node.
+//
+// Node 22/23 need the --experimental-async-context-frame opt-in. Node 24
+// turned ACF on by default and *removed* the flag, so passing it there is a
+// hard `node: bad option` failure rather than a no-op. Anything that spawns a
+// Node process for these tests has to compute the list rather than hardcode
+// it; that includes `npm test` itself (see run.js).
+function acfFlags() {
+    const major = Number(process.versions.node.split('.')[0]);
+    return major >= 22 && major < 24 ? ['--experimental-async-context-frame'] : [];
+}
+
+module.exports = { acfFlags };

js/test/run.js

@@ -0,0 +1,36 @@
+'use strict';
+
+// `npm test` entry point.
+//
+// The script used to pass --experimental-async-context-frame unconditionally,
+// which works on Node 22/23 and fails outright from Node 24 on, where the flag
+// was removed:
+//
+//     node: bad option: --experimental-async-context-frame
+//
+// so `npm test` was broken on every current Node. Compute the flags instead.
+
+const { spawnSync } = require('node:child_process');
+const path = require('node:path');
+
+const { acfFlags } = require('./node-flags');
+
+const major = Number(process.versions.node.split('.')[0]);
+const flags = [...acfFlags()];
+// --disable-warning landed in Node 21.3; on older Node it would itself be a
+// bad option. Nothing below 22 can run these tests anyway (test.js bails).
+if (major >= 22) {
+    flags.push('--disable-warning=ExperimentalWarning');
+}
+
+const res = spawnSync(
+    process.execPath,
+    [...flags, '--test', path.join(__dirname, 'test.js')],
+    { stdio: 'inherit' },
+);
+
+if (res.error) {
+    console.error(res.error);
+    process.exit(1);
+}
+process.exit(res.status === null ? 1 : res.status);