Stream Issues #1376

•
framework/packages/stream/src/PhpInputStream.php:32: getInstance() never assigns self::$instance, so it never caches.
•
src/StringStream.php:263: write() ignores isWritable(), so writable(false) doesn't block writes.
•
src/StringStream.php:323: getContents() doesn't advance the position, unlike Stream.
•
src/DecoratorStream.php:16: a null target leaves the typed property uninitialized.