Rework vkwave.bots.core.dispatching.cast

[prostomarkeloff]

Getting cast by type(value) looks bad.
It should have list of handlers that will inspect object each by each and if handlers don't return any cast, caster will run default implementation.

def cast(self, obj: typing.Any):
    result = self.from_handlers(obj) or self.default(obj)
    return result