fix(controller): default $socketIds in whisper() to silence PHP 8.x deprecation

Optional parameter $payload (and $event) declared before required
parameter $socketIds is implicitly treated as required by PHP 8.4+,
emitting a deprecation on every class load:

  PHP Deprecated: Optional parameter $payload declared before
  required parameter $socketIds is implicitly treated as a required
  parameter

Made $socketIds optional (= []) — empty matches no connections via
array_flip lookup, so callers that intentionally omit it get a no-op
which preserves the practical contract (you can't whisper to nobody).
All four parameters are now optional. No call-site changes needed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Websocket/Controller.php

@@ -473,9 +473,14 @@ class Controller
     final public function whisper(
         array|string|null $payload = null,
         ?string $event = null,
-        array $socketIds,
+        array $socketIds = [],
         ?string $channel = null
     ) {
+        // PHP 8.x deprecates "optional before required" in parameter
+        // lists, so $socketIds is now defaulted. Empty $socketIds is a
+        // no-op (the array_flip-based lookup below matches no
+        // connections), preserving the existing behavior for callers
+        // that intentionally omit it.
         if (is_string($payload)) {
             $payload = [
                 'message' => $payload,