fix(runtime): use private synchronization lock for ActivationData

[ReubenBond]

Summary

• Adds a private synchronization lock to ActivationData and uses it instead of locking on the activation instance.
• Routes external activation-locking call sites (ActivationCollector, activation migration acceptance, and incoming request monitoring) through the same synchronization lock.
• Gives activation command cancellation/disposal its own private lock instead of locking on the command object.

Validation

• git diff --check HEAD^ HEAD
• conflict-marker scan
• dotnet build src\Orleans.Runtime\Orleans.Runtime.csproj -m --no-restore -v:q
• dotnet test test\Orleans.Core.Tests\Orleans.Core.Tests.csproj --filter FullyQualifiedName~ActivationCollectorTests (28 passed; existing xUnit serialization warnings only)

Notes

• No collection ticket algorithm changes are included.
• Review focus: activation collection versus deactivation races, lock ordering, and no deadlock regressions.

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull request overview

This PR updates Orleans Runtime activation synchronization by introducing a private lock object on ActivationData and routing external activation-locking call sites to use it, instead of locking on activation instances or command objects. This aims to reduce accidental lock coupling and make activation state synchronization more explicit and controllable across the runtime.

Changes:

• Added a private synchronization lock to ActivationData and replaced lock(this) with lock(_lock) for mutable activation state.
• Updated external call sites (ActivationCollector, activation migration acceptance, and incoming request workload monitoring) to lock using the activation synchronization lock.
• Updated activation command cancellation/disposal synchronization to use a private lock object instead of locking on the command instance.

Show a summary per file

File	Description
src/Orleans.Runtime/Catalog/IncomingRequestMonitor.cs	Uses activation.SynchronizationLock when analyzing activation workload.
src/Orleans.Runtime/Catalog/ActivationMigrationManager.cs	Uses activation.SynchronizationLock when polling activation state during migration acceptance.
src/Orleans.Runtime/Catalog/ActivationData.cs	Introduces _lock, exposes SynchronizationLock, replaces internal lock(this) usage, and adds GetSynchronizationLock helper for collector call sites.
src/Orleans.Runtime/Catalog/ActivationCollector.cs	Locks collectible contexts via ActivationData.GetSynchronizationLock(...) instead of locking on the context instance.

Copilot's findings

• Files reviewed: 4/4 changed files
• Comments generated: 0