[CodeQuality] Add WillReturnCallbackFallbackToThrowRector

[TomasVotruba]

Adds a rule that turns the unreachable fallback return of a consecutive willReturnCallback() into a throw, so an unexpected extra call fails loudly instead of silently returning a stale value.

After withConsecutive() is migrated to a matcher willReturnCallback(), the trailing return is a leftover of the original single willReturn() — it is reached only when the mock is called more often than expected. Returning there hides the over-call; throwing surfaces it.

 $this->someServiceMock->expects($matcher)
     ->method('run')
     ->willReturnCallback(function () use ($matcher) {
         if ($matcher->numberOfInvocations() === 1) {
             return 'first';
         }

         if ($matcher->numberOfInvocations() === 2) {
             return 'second';
         }

-        return 'second';
+        throw new \PHPUnit\Framework\Exception(sprintf('Method should not be called for the %dth time', $matcher->numberOfInvocations()));
     });

Only fires when the closure uses $matcher, branches on its invocation count, and ends with an unconditional return. Added to the phpunit-code-quality set.