feat(directory): add cancellation-aware operations

[ReubenBond]

Grain directory callers cannot currently propagate cancellation into directory implementations, so activation shutdown can leave registration work running and stale registrations are replaced non-atomically.

Add backward-compatible cancellation overloads with default cancelable waits, implement linked shutdown/caller cancellation in the distributed directory, propagate activation cancellation through the locator stack, and conditionally replace stale registrations in one register operation.

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull request overview

This PR adds cancellation-aware directory operations so callers (notably activation shutdown paths) can propagate cancellation into grain directory implementations, reducing lingering work during shutdown and improving stale registration replacement behavior in the locator stack.

Changes:

• Adds backward-compatible CancellationToken overloads to IGrainDirectory (with default cancelable waits) and updates the public API surface.
• Propagates cancellation through GrainLocator into CachedGrainLocator, and updates activation registration to pass cancellation directly.
• Updates the distributed grain directory to link caller cancellation with shutdown cancellation, and adjusts tests for the new conditional replace behavior.

Show a summary per file

File	Description
test/Orleans.Core.Tests/Directory/IGrainDirectoryTests.cs	Adds coverage ensuring new cancellation overloads default to cancelable waits.
test/Orleans.Core.Tests/Directory/CachedGrainLocatorTests.cs	Updates mocks/expectations for new cancellation overload usage and conditional replace registration flow.
src/Orleans.Runtime/GrainDirectory/GrainLocator.cs	Adds cancellation support to registration flow and forwards to cached locator when applicable.
src/Orleans.Runtime/GrainDirectory/DistributedGrainDirectory.cs	Introduces cancellation overloads and links caller cancellation with shutdown token.
src/Orleans.Runtime/GrainDirectory/CachedGrainLocator.cs	Propagates cancellation into directory register operations and switches to conditional replace semantics.
src/Orleans.Runtime/Catalog/ActivationData.cs	Passes activation cancellation token into grain locator registration.
src/Orleans.Core.Abstractions/GrainDirectory/IGrainDirectory.cs	Adds cancellation-token overloads as default interface methods for backward compatibility.
src/api/Orleans.Core.Abstractions/Orleans.Core.Abstractions.cs	Updates generated API surface to include the new overloads.

Copilot's findings

• Files reviewed: 8/8 changed files
• Comments generated: 4