fix: fix Mercure assertions to public to allow Mercure Hub reset

[vincentchalamon]

Q	A
Branch?	main
Tickets	N/A
License	MIT
Doc PR	TODO

Creating fixtures on functional tests may send Mercure Update objects. Before executing the test calls, the developer should be able to reset the Mercure Hub:

public function testAsAdminUserICanUpdateABook(): void
{
    FooFactory::createOne();
    self::getMercureHub()->reset();    // <== this line resets the Mercure Hub

    $this->client->request(...);
    self::assertCount(1, self::getMercureMessages());
}

• fix Mercure assertions to public to allow Mercure Hub reset
• decorate Mercure Hub for test performance

[vincentchalamon]

Currently the Mercure assertions are based on the TraceableHubRegistry only enabled with debug mode. I'm facing performance issues using debug mode on tests (Allowed memory size..., cf. https://github.com/api-platform/demo/actions/runs/6225295170/job/16895399919) on Doctrine and Apcu because of this debug mode.

I'm thinking about decorating the Mercure HubRegistry to create a custom one just for this use-case (tests), which avoid enabling the debug mode in tests.

WDYT @soyuka?