[Mime] Deprecate implementing __sleep/wakeup() on AbstractPart implementations

Author: nicolas-grekas

AbstractString.php

@@ -708,7 +708,7 @@ public function wordwrap(int $width = 75, string $break = "\n", bool $cut = fals
 
     public function __serialize(): array
     {
-        if (self::class === (new \ReflectionMethod($this, '__sleep'))->class) {
+        if (self::class === (new \ReflectionMethod($this, '__sleep'))->class || self::class !== (new \ReflectionMethod($this, '__serialize'))->class) {
             return ['string' => $this->string];
         }
 

LazyString.php

@@ -103,7 +103,7 @@ public function __toString(): string
 
     public function __serialize(): array
     {
-        if (self::class === (new \ReflectionMethod($this, '__sleep'))->class) {
+        if (self::class === (new \ReflectionMethod($this, '__sleep'))->class || self::class !== (new \ReflectionMethod($this, '__serialize'))->class) {
             $this->__toString();
 
             return ['value' => $this->value];

UnicodeString.php

@@ -368,7 +368,7 @@ public function startsWith(string|iterable|AbstractString $prefix): bool
 
     public function __unserialize(array $data): void
     {
-        if ($wakeup = self::class !== (new \ReflectionMethod($this, '__wakeup'))->class) {
+        if ($wakeup = self::class !== (new \ReflectionMethod($this, '__wakeup'))->class && self::class === (new \ReflectionMethod($this, '__unserialize'))->class) {
             trigger_deprecation('symfony/string', '7.4', 'Implementing "%s::__wakeup()" is deprecated, use "__unserialize()" instead.', get_debug_type($this));
         }