vfs: speed up recursive readdir test setup

Create the deep directory tree with one recursive mkdirSync() call.
This avoids repeatedly resolving increasingly long paths and prevents
timeouts on slower CI hosts.

Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com>
Assisted-by: codex:gpt-5.6-sol
PR-URL: #64813
Refs: https://github.com/nodejs/reliability/issues?q=sort%3Aupdated-desc%20%22test-vfs-readdir-symlink-recursive%22
Reviewed-By: Aviv Keller <me@aviv.sh>
Reviewed-By: Tim Perry <pimterry@gmail.com>

Author: trivikr

test/parallel/test-vfs-readdir-symlink-recursive.js

@@ -114,12 +114,8 @@ assert.ok(
   const v = vfs.create();
 
   // Build /deep/0/1/2/.../999/leaf.txt
-  let path = '/deep';
-  v.mkdirSync(path);
-  for (let i = 0; i < DEPTH; i++) {
-    path += `/${i}`;
-    v.mkdirSync(path);
-  }
+  const path = `/deep/${Array.from({ length: DEPTH }, (_, i) => i).join('/')}`;
+  v.mkdirSync(path, { recursive: true });
   v.writeFileSync(`${path}/leaf.txt`, 'deep');
 
   const entries = v.readdirSync('/deep', { recursive: true });