Added ability to specify class/instance methods as callbacks

[sergix44]

Hi!
This PR add the ability to specify commands/callbacks as class+method references: right now the framework supports only closures:

$bot = new Zanzara("YOUR-BOT-TOKEN");

$bot->onCommand('start', function (Context $ctx) {
    $ctx->sendMessage('Hello');
});

$bot->run();

With this PR also this is possible:

$bot = new Zanzara("YOUR-BOT-TOKEN");

$bot->onCommand('start', [StartCommand::class, 'startMethod']);

$bot->run();

[cheeghi]

Hi! Thank you for the PR.
Cool feature, I took a look at the changes, they seem clean and well tested. Just one thing, I've seen that you changed the hierarchy of Zanzara, ListenerResolver and ListenerCollector, I suppose you made it to have the container instance available in ListenerCollector, but I don't like the idea of a superclass (ListenerResolver) using a field ($listeners) of its subclass (ListenerCollector). Instead, I would keep ListenerResolver extending ListenerCollector and move the $container field in ListenerCollector.
We use a gitflow workflow so I change the target branch to develop.

[sergix44]

Hi! Thank you for the PR.
Cool feature, I took a look at the changes, they seem clean and well tested. Just one thing, I've seen that you changed the hierarchy of Zanzara, ListenerResolver and ListenerCollector, I suppose you made it to have the container instance available in ListenerCollector, but I don't like the idea of a superclass (ListenerResolver) using a field ($listeners) of its subclass (ListenerCollector). Instead, I would keep ListenerResolver extending ListenerCollector and move the $container field in ListenerCollector.
We use a gitflow workflow so I change the target branch to develop.

Done in last commit

[cheeghi]

Hi, we are adding php 8 support for zanzara and unit tests for this feature fail under php 8. In php 8 the array [MyType::class, 'myMethod'] is considered callable only if 'myMethod' is static, otherwise you must provide an array [$myTypeInstance, 'myMethod'] where the method can be non-static. I think it's a bit ugly delegating the class instantiation to the user. We may get rid of the is_callable check (since later the call actually works because we instantiate the class through the container) or we may improve the check. Can you have a look at it? Thanks! (you can fork the feature/php-8 branch).

Edit: I didn't notice last time: the testWithClass method defines two listeners for the start command, but actually zanzara doesn't support (at the moment, may be useful to implement in the future) multiple listeners for a specific command. So only the assertions of $bot->onCommand('start', [TestCommandClassNoConstructor::class, 'start']); are performed, while those of $bot->onCommand('start', [TestCommandClassWithConstructor::class, 'start']); are ignored. You may split the test in two methods.

[sergix44]

It should be ok, just check if it is a callable first (so static::class + static method), if this is not a callable then if the object instantiated via DI + method is that a callable, if none of these conditions are true then it probably was not defined correctly. Or ye, get rid of the check entirely.