Support IsLocked and LockAsync for Entities

Durable Functions for .NET supports mutual exclusion for entity code. We need to investigate how to enable this feature in OOProc and to provide the APIs for it.

After an initial investigation, we'll update this ticket with more implementation details

The issue names OOProc and the IsLocked/LockAsync APIs but no files, entry points, or tests. Start by investigating how Durable Functions for .NET provides entity mutual exclusion and how OOProc handles entities; done means the ticket has concrete implementation details for the APIs and their validation.

Written by the indexing model from the issue text.