Use `Optional<T>` and similar for optional command arguments

[Strokkur424]

Is your feature request related to a problem?

Currently, if one would want to add optional arguments, they would need to create multiple methods with the same semantics, which call each other:

@Executes
void run(ItemType type) {
  run(type, 1, player);
}

@Executes
void run(ItemType type, int count) {
  run(type, count, "Default name");
}

@Executes
void run(ItemType type, int count, String name) {
  // ...
}

It is not far fetched to say that this is repetitive and annoying.

Describe the solution you'd like.

Instead, parameters wrapped in Optional<T> (or one of the similar types, like OptionalInt) can be provided at the end of the parameter list for values that do not have to be present:

@Executes
void run(ItemType type, OptionalInt count, Optional<String> name) {
  int actualCount = count.orElse(1);
  String actualName = name.orElse("Default name");
  // ...
}

Describe alternatives you've considered.

No response

Other

For the primitive types and String, annotations for the default value could also be provided (@DefaultInt(1) or @DefaultString("Default name")), which would circumvent the usage of Optional for these, however the Optional<T> way would be very convenient for complex types, like World objects.