feat: add cancelPairingCode() and requestPairingCode() on QR clients (#22449)

* feat: add cancelPairingCode() and allow requestPairingCode()

- requestPairingCode() now exposes onCodeReceivedEvent if needed,
  so it works on clients initialized in QR mode
- Add cancelPairingCode() method to stop pairing and return to QR
- Update TypeScript definitions

* fix(auth): dynamic ADV key in getQR + structural cancelPairingCode

the getQR closure captured advSecretKey once during initialize(), but
requestpairingcode/cancelPairingCode changes the key in IndexedDB.
the stale closure key caused QR scans to fail with HMAC validation error.

fix: read key dynamically via WAWebUserPrefsMultiDevice.getADVSecretKey()
(synchronous in-memory cache) on every getQR call, matching how WhatsApp
web's internal QR component works.

cancelpairingcode now mirrors WhatsApp Web's resetLinkDeviceState:
refreshqr() restarts WebSocket for fresh refs, then
initializeqrlinking() generates a new key. QR emission happens
automatically via the existing change:ref listener.

---------

Co-authored-by: BenyFilho <168232825+BenyFilho@users.noreply.github.com>

index.d.ts

@@ -197,6 +197,9 @@ declare namespace WAWebJS {
             intervalMs?: number,
         ): Promise<string>;
 
+        /** Cancels an active pairing code session and returns to QR code mode */
+        cancelPairingCode(): Promise<void>
+
         /** Force reset of connection state for the client */
         resetState(): Promise<void>;