fix cors function for alpine linux (#4091)

I provide docker images with alpine linux and tested the new cors
approach.

It didn't work because after calling

```js
  const dispatcher = new Agent({ connect: { lookup: (_h, _o, cb) => cb(null, address, family) } });
```

the dispatcher variable was undefined.

This PR solves this and I tested this under debian too.

The mix of internal fetch and newer undici did not work and alpine needs
additionally the `process.nextTick`.

---------

Co-authored-by: Kristjan ESPERANTO <35647502+KristjanESPERANTO@users.noreply.github.com>

js/server_functions.js

@@ -2,7 +2,7 @@ const dns = require("node:dns");
 const fs = require("node:fs");
 const path = require("node:path");
 const ipaddr = require("ipaddr.js");
-const { Agent } = require("undici");
+const undici = require("undici");
 const Log = require("logger");
 
 const startUp = new Date();
@@ -98,9 +98,16 @@ async function cors (req, res) {
 			}
 
 			// Pin the validated IP — fetch() reuses it instead of doing its own DNS lookup
-			const dispatcher = new Agent({ connect: { lookup: (_h, _o, cb) => cb(null, address, family) } });
+			const dispatcher = new undici.Agent({
+				connect: {
+					lookup: (_h, _o, cb) => {
+						const addresses = [{ address: address, family: family }];
+						process.nextTick(() => cb(null, addresses));
+					}
+				}
+			});
 
-			const response = await fetch(url, { dispatcher, headers: headersToSend });
+			const response = await undici.fetch(url, { dispatcher, headers: headersToSend });
 			if (response.ok) {
 				for (const header of expectedReceivedHeaders) {
 					const headerValue = response.headers.get(header);

tests/unit/functions/server_functions_spec.js

@@ -1,9 +1,10 @@
-// Tests use vi.spyOn on shared module objects (dns, global.fetch).
+// Tests use vi.spyOn on shared module objects (dns, undici).
 // vi.spyOn modifies the object property directly on the cached module instance, so it
 // is intercepted by server_functions.js regardless of the Module.prototype.require override
 // in vitest-setup.js.  restoreAllMocks:true auto-restores spies, but may reuse the same
 // spy instance — mockClear() is called explicitly in beforeEach to reset call history.
 const dns = require("node:dns");
+const undici = require("undici");
 const { cors, getUserAgent, replaceSecretPlaceholder } = require("#server_functions");
 
 describe("server_functions tests", () => {
@@ -41,7 +42,7 @@ describe("server_functions tests", () => {
 
 			// vi.spyOn may return the same spy instance across tests when restoreAllMocks
 			// restores-but-reuses; mockClear() explicitly resets call history each time.
-			fetchSpy = vi.spyOn(global, "fetch");
+			fetchSpy = vi.spyOn(undici, "fetch");
 			fetchSpy.mockClear();
 			fetchSpy.mockImplementation(() => Promise.resolve({
 				headers: { get: fetchResponseHeadersGet },