fix(logger): accept any Monolog handler as process manager log writer

[jremmurd]

Problem

AbstractLogger::createStreamHandler() is typed StreamHandler | ApplicationLoggerDb | null, but its only consumer is MonitoringItem::getLogger():

$streamHandler = $obj->createStreamHandler($loggerConfig, $this);
if ($streamHandler) {
    $this->logger->addWriter($streamHandler);
}

ApplicationLogger::addWriter(object $writer) accepts every HandlerInterface implementation. The declared union is therefore narrower than what the bundle actually supports, and it rules out every Monolog handler that does not happen to extend StreamHandler: the AsyncAws CloudWatch handler, Sentry, Slack, Redis, and so on.

That ApplicationLoggerDb is already part of the union, and is not a StreamHandler, shows the intent was "a log writer", not "a stream".

A project cannot work around this. The return type of an overriding method may only be narrowed, never widened, so returning a non-stream handler is impossible. In our case the custom CloudWatch logger had to return null to satisfy the signature, which silently disabled process manager logging to CloudWatch: getLogger() drops a null writer without a warning.

Change

Widen the abstract return type to ?HandlerInterface, drop the two imports that become unused.

Backwards compatible. All four shipped implementations keep their current, narrower return types, which covariance allows:

• File — ?StreamHandler
• Console — ?StreamHandler
• EmailSummary — ?StreamHandler
• Application — ApplicationLoggerDb

Project implementations that already return one of those types are unaffected.

The method name stays createStreamHandler() to avoid a breaking rename.

Branches

The same commit is proposed for pimcore12 in a separate PR, the file is identical on both branches.