Review interface of manipulators about hearthstone-ai HOT 6 CLOSED

• manipulators should not let client card to add event at any moment
• an event can only be registered if it will be correct when
  • the minion got silenced
  • the minion got copied
• the lifetime of an enchantment
  • lifetime begins at
    • minion is summoned
    • minion is copied
    • call 'AfterAdded()'
  • lifetime ends at
    • minion is silenced
    • minion is not in hand/play zone
    • call 'AfterRemoved'
      • but the registered event cannot be removed here (limited of event manager)

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Solutions

1. Event manager should be able to remove a specified event trigger
   • so an enchantment bound with an event can un-register that event when got silenced
2. implement enchantment card as another state::Cards::Card

• when enchantment is removed, also removed the card from PLAY zone to GRAVEYARD zone
• when the event is triggered, check the associate enchantment card

from hearthstone-ai.

A class called EventListener
A minion can have several EventListener
Methods of EventListener:

1. Register
2. Unregister

Event manager should return event identifier so caller can remove it afterwards

Card manipulator provides interface to add an event listener

Each enchantment is a kind of event listener
It might listen to nothing
In this case, the unregister callback is a nullptr

Aura and enchantment are both a kind of event listener
Maybe we can unify them

When a minion is silenced, all its enchantment and aura are removed
That is, the event listeners are removed

When a minion is copied
The event listener are either removed, or reregistered

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EventListener can be written in namespace state
maybe right aside to the event manager

maybe the 'added_to_zone' callback can be removed

state::ZoneChanger invoke the 'register' and 'unregister' methods of the event listeners
maybe define a compile-time template enum to states the lifetime policy

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Decided not to remove a attached event. An event can only be removed by itself.

A event-hooked enchantment will be implemented.
Such enchantments should be with a play order. And the field 'silenced' should become 'silenced_at_play_order'. So the event callback can check if it is silenced.

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Event-hooked enchantment is fixed in commits: ab6ab60 b1e2108 9e905e2

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