[CodeQuality] Handle return throw and return null in void mock callbacks

[TomasVotruba]

When a mocked void method's willReturnCallback() closure mixes return null; with a return throw new X;, RemoveReturnFromVoidMethodMockCallbackRector bailed out (a return throw is not a "pure" value), so it stripped nothing and typed nothing. TypeWillReturnCallableArrowFunctionRector then added : void on its own, leaving the value returns in place — producing code that fatals:

PHP Fatal error: A void function must not return a value

Note return throw new X; is also illegal in a void function, so stripping only return null; is not enough — the return must be dropped from the throw too.

This makes the rule normalize the whole void closure instead of bailing:

• return null; (and other pure returns) → return;
• return throw new X; → throw new X;
• closure typed : void

Impure, non-throw value returns still bail safely (behavior unchanged).

Before → After

             ->method('persist')
-            ->willReturnCallback(function ($entity) use ($matcher) {
+            ->willReturnCallback(function ($entity) use ($matcher): void {
                 if (1 === $matcher->numberOfInvocations()) {
-                    return null;
+                    return;
                 }

                 if (2 === $matcher->numberOfInvocations()) {
-                    return throw new \RuntimeException('boom');
+                    throw new \RuntimeException('boom');
                 }
             });