feat(journaling): select journal providers per grain type

[ReubenBond]

Summary

Enable a grain type to select a registered named journal storage provider. All journaled state in an activation should use that provider through the activation's shared journaled state manager.

Follow-up to #11275, which introduces named journal provider registration and keyed storage, catalog, and state-manager factory services.

Motivation

Applications need different grain types to use independent journal namespaces, accounts, or backends while retaining a default provider for other types. A grain-type declaration should connect those named registrations to ordinary DurableGrain usage and injected durable state.

Today, DurableGrain resolves the activation-scoped, unkeyed IJournaledStateManager. Its registration resolves the unkeyed IJournalStorageProvider, supplied by the Default binding. Named factories support explicit journal consumers; grain activations currently select the default provider.

Proposed behavior

• Provide a declarative grain-type provider selection mechanism, integrated with Orleans grain-type metadata and existing configuration conventions. Evaluate the existing storage-provider attribute conventions when choosing the public API.
• Resolve the selected named provider when creating the activation-scoped journaled state manager. Keep the selection consistent across silos and stable for the activation's lifetime.
• Use the same manager and selected storage for DurableGrain.StateManager, injected durable values and collections, and journaling-backed persistent state.
• Preserve Default selection for grain types without an explicit selection, including its existing unnamed backend-options behavior.
• Report an invalid or unregistered selection clearly, identifying the grain type and provider name, before accessing journal data.
• Preserve journal identity derivation and the provider registration's options and lifecycle semantics.

Acceptance criteria

• Two grain types can select different providers, including two named providers of the same backend, and recover their respective state after deactivation and reactivation.
• Grain types without an explicit selection continue to use Default, independent of named-provider registration order.
• A grain's base-class operations and all injected journaled state share the same activation-scoped manager and selected provider.
• Invalid provider selections produce contextual configuration errors rather than selecting another provider.
• Regression coverage verifies provider isolation, default compatibility, activation lifecycle/recovery, and invalid selections on supported target frameworks.
• Public APIs have XML documentation and regenerated API surfaces where applicable.
• Documentation includes a compilable per-grain-type configuration example and explains that recovery reads the selected physical namespace. Changing the selection for a grain type with existing journals requires a deliberate data migration or cutover strategy.

Implementation entry points

• src/Orleans.Journaling/HostingExtensions.cs: activation-scoped manager registration and named provider bindings.
• src/Orleans.Journaling/DurableGrain.cs: manager resolution and grain lifecycle participation.
• src/Orleans.Journaling/JournaledStateManager.cs: grain journal identity and provider-backed storage creation.

Keep the change focused on selecting providers for grain types; retain the named-provider registration behavior established by #11275.