feat: add GetAllEntities API

[2vg]

close: #57

• Add GetAllEntities/GetAllEntitiesByClassname methods to IEntityManager for retrieving all currently existing entities
• Maintain an internal entity cache in EntityManager using an index-based array and a uint[] bitset, populated via existing OnEntityCreated/OnEntityDeleted callbacks
• Entity references are stored in a fixed IBaseEntity?[16384] array indexed by EntityIndex
• A uint[512] bitset tracks which indices are active, enabling fast enumeration via BitOperations.TrailingZeroCount without scanning empty slots
  • BitOperation should make it run faster than a naive implementation, Because empty buckets can be skipped, it can be iterated in O(active) time in a sparse state
• As a bonus, fixed some LogError typos.

Added

• GetAllEntities(): Returns all active entities
• GetAllEntities<T>(): Returns all active entities matching a specific type
• GetAllEntitiesByClassname(string classname): Returns all active entities matching a classname (useful for entity types without a dedicated interface, e.g. CPropYadaYada)
• GetAllEntitiesByClassname<T>(string classname): Returns all active entities matching both a classname and a specific type

[2vg]

I asked nuko-sama, and they told me that Created/Destroy is the best option.
Please let me know if there's a better way. 🙏

[Nukoooo]

just some nitpicks, it looks good to me

[Kxnrl]

an entity will fire an OnDeleted event when it is marked as KILL_ME, but at this time the entity is not destroyed and its data/proterties can be safely accessed. I think you might need to consider this special case, as it is quite common with weapon and item entities. OnDeleted even getting fired before OnSpawned.

[2vg]

@Kxnrl I've moved it to DeletedPost for now.
Even if retrieved from the cache, I think the Entity should be checked by the Developer using IsValid, etc., but I'm not sure what the best solution is.