ConstThe Proxy object allows us to define a handler that will intercept
the property access and return an empty array if the property does not exist in the object.
This means that accessing signatureSpecies will not throw an error if the property does not exist,
but instead default to an empty array.
The signature species for each Gym Leader, Elite Four member, and Champion. The key is the trainer type, and the value is an array of Species or Species arrays. This is in a separate const so it can be accessed from other places and not just the trainerConfigs