add method
Implementation
Future<T?> add(T t,{bool addToState=true, bool toLast=true})async{
DocumentReference doc;
try{
doc=await fbCol.add(config.toDocWithId(t)..remove(idKey));
}on FirebaseException catch(e){
config.onException(e);
return null;
}
final r = config.setId(t,doc.id);
if(addToState&&mounted) {
state=state.whenData((v) => List.of(addMore(v,[r],toLast: toLast)));
}
return r;
}