Fix Client::setProtocol() always throwing

[tomsommer]

Client::setProtocol() could never succeed:

• it stored the protocol class name ($obj) instead of the given instance, and
• after the matching type was found, break fell through to the throw, so every call threw InvalidServiceDefinitionException: Service protocol "..." is not supported.

Now the instance is stored and the method returns once a matching protocol type is found. An unsupported protocol still throws.

$client = new Client();
$protocol = new DomainProtocol($client, $myDomainService);
$client->setProtocol($protocol);
$client->getProtocol(Client::DOMAIN) === $protocol; // true, previously threw

phpcs and phpstan pass.