Unable to implement reminders for my own StateProvider implementation

[ssteinau]

Describe the bug
ActorService allows implementing custom actor state providers. The Interface IActorStateProvider requires implementing the method

    Task<ReminderPagedResult<KeyValuePair<ActorId, List<ActorReminderState>>>> GetRemindersAsync(
        int numItemsToReturn, ...); // parameters omitted for brevity

The problem is in the return type "List<ActorReminderState>". ActorReminderState is public non-sealed class and as such can be subclassed, yet its constructor is internal - One cannot create instances of the subclass.

Related issues cascade through the code as well:.ActorStateReminder constructor parameters are internal classes as well,
To Reproduce

Create new project, import the actors NuGet package, create a subclass of ActorReminder state with a 3-param constructor that calls the base class. Compiler error because the base class constructor is internal. Example:

public class SubActorReminderState : ActorReminderState, IActorReminderState
{

  /*Properties
  */
  //Constructor
    public SubActorReminderState(ActorReminderData reminder, TimeSpan currentLogicalTime, ReminderCompletedData reminderCompletedData) : base(reminder,currentLogicalTime,reminderCompletedData) //calling base gives compiler error

Expected behavior

Be able to implement reminders for the state provider.
Possible solutions:

• Make the ActorReminderState constructor and parameter classes public
• Make GetRemindersAsync return List<IActorReminderState>

Additional context

• There is an Interface IActorReminderState that ActorReminderState implements. The new signature of GetRemindersAsync could be

    Task<ReminderPagedResult<KeyValuePair<ActorId, List<IActorReminderState>>>> GetRemindersAsync(
        int numItemsToReturn, ...); // parameters omitted for brevity
  

and a user can then implement the IActorReminderState interface, ActorReminderState can stay as-is.

Caveat: the interface would have to include additional properties and methods, non-interface properties and methods of ActorReminderState are used throughout the project.