Add unit tests for data file rotation utility functions

- Implement tests for writing data files with rotation, ensuring backups are created only on changes.
- Verify that old backups are rotated correctly and the maximum number of backups is maintained.
- Test restoration of backups while preserving the current state as a backup.
- Utilize Vitest for testing framework and manage temporary file storage during tests.

server/utils/contact-requests.js

@@ -1,6 +1,7 @@
 import { promises as fs } from 'fs'
 import path from 'path'
 import { randomUUID } from 'crypto'
+import { writeDataFileWithRotation } from './data-file-rotation.js'
 
 // nosemgrep: javascript.lang.security.audit.path-traversal.path-join-resolve-traversal.path-join-resolve-traversal
 // filename is always a hardcoded constant, never user input
@@ -29,7 +30,7 @@ export async function readContactRequests() {
 }
 
 export async function writeContactRequests(items) {
-  await fs.writeFile(CONTACT_REQUESTS_FILE, JSON.stringify(items, null, 2), 'utf-8')
+  await writeDataFileWithRotation(CONTACT_REQUESTS_FILE, JSON.stringify(items, null, 2), { encoding: 'utf-8' })
 }
 
 export async function createContactRequest(data) {