Convert EditFailedMessageManager to an atomic write operation

[rbev]

This pull request refactors and simplifies the "edit failed message" workflow in both EF Core and RavenDB persistence implementations. It removes the manager/session-based pattern in favor of explicit, atomic data store operations, clarifies persistence guidelines, and updates tests to match the new approach. The result is clearer, more robust, and easier-to-maintain persistence APIs for editing failed messages.

Persistence API refactoring and simplification:

• Replaces the EditFailedMessagesManager and session-based workflow in both EF Core and RavenDB with direct, atomic methods (TryBeginEdit, GetCurrentEditingRequestId) on the data store classes, eliminating the need for manager objects and implicit state. [1] [2] [3] [4]

Concurrency and atomicity improvements:

• Ensures that edit-acquisition operations are atomic and handle concurrency conflicts explicitly, with provider-specific exception handling and clear domain outcomes (e.g., reporting if another edit has already been acquired). [1] [2]

Documentation updates:

• Adds new guidelines to the coding and design documentation, recommending explicit persistence operations over generic session managers and describing best practices for atomic operations and unit-of-work APIs.

Test updates and coverage:

• Refactors and renames tests to match the new API, ensuring that timestamping and edit-acquisition logic are properly validated for both EF Core and RavenDB, and adds new tests for RavenDB expiration behavior. [1] [2] [3] [4]

Code cleanup:

• Removes obsolete manager/session classes and related abstractions that are no longer needed after the refactor. [1] [2]

[johnsimons]

This is so much nicer