Plugged method should plug without a callback #35

Right now when you create a plug and apply it.

eg.

var methodPlug = Nasal.Method(Method);
var propertyPlug = Nasal.Property<string>(Property)
//...
using var _ = Nasal.ApplyAsync(methodPlug, propertyPlug);

These plugs are not applied because a callback/return have not been set on them. These then end up doing nothing. These should instead default to empty callbacks (or throwing callbacks) to provide more expected default behavior.