Replace ReplicationProgressHandler with IProgress<T>

[MichaelGrafnetter]

Summary

• Replaces the custom ReplicationProgressHandler delegate on DirectoryReplicationClient with the standard IProgress<ReplicationProgress> interface across GetAccounts, ReplicateAllObjects, and FetchFullSchema.
• Adds optional CancellationToken parameters so long-running replication can be cancelled cooperatively between DRS cycles.
• Wires Get-ADReplAccount to surface Ctrl+C as cancellation and to convert OperationCanceledException into a clean progress completion.

Why

The custom delegate predates wide adoption of System.IProgress<T>. Switching aligns the public DSInternals.Replication API with idiomatic .NET conventions, pairs naturally with CancellationToken, and makes the surface self-documenting for external consumers.

Notes for reviewers

• Breaking change in DSInternals.Replication: callers of the affected methods must migrate from ReplicationProgressHandler to IProgress<ReplicationProgress>. The new ReplicationProgress payload keeps the same data the old delegate received (Cookie, ProcessedObjectCount, TotalObjectCount) so external consumers that need the cookie for resumable replication keep working after a one-line adapter. Documented under ### Changed in Documentation/CHANGELOG.md.
• A new internal SynchronousProgress<T> helper is intentionally used instead of the BCL Progress<T>: PowerShell cmdlets must call WriteProgress on the pipeline thread, but Progress<T> marshals through the captured SynchronizationContext (or the thread pool when none is present), which would move the callback off the pipeline thread.
• Cancellation is checked between DRS round-trips only — the native DRS call itself is not interruptible. This matches the prior Ctrl+C experience and is intentional.
• CancellationTokenSource is scoped to GetADReplAccountCommand rather than the shared ADReplCommandBase, since it is the only cmdlet that needs it today.

Test plan

• dotnet build DSInternals.DotNetSdk.slnf (Release, x64) — 0 errors
• dotnet test --solution DSInternals.DotNetSdk.slnf
• Manual smoke: Get-ADReplAccount -All against a lab DC — progress advances; Ctrl+C completes cleanly
• Manual smoke: Get-ADReplAccount -All -Properties LAPS — schema progress (activity 2) still renders
• Manual smoke: Get-ADReplAccount -SamAccountName Administrator — non-bulk path still works
• pwsh -File Scripts/Invoke-SmokeTests.ps1 -Configuration Debug

[Copilot]

Pull request overview

Replaces the bespoke ReplicationProgressHandler delegate with the idiomatic IProgress<ReplicationProgress> interface across DirectoryReplicationClient's replication methods, and adds optional CancellationToken parameters for cooperative cancellation between DRS cycles. The Get-ADReplAccount cmdlet is wired up to translate Ctrl+C into cancellation and to convert OperationCanceledException into a clean progress completion.

Changes:

• Introduce ReplicationProgress record struct and remove the legacy delegate.
• Update GetAccounts, ReplicateAllObjects, and FetchFullSchema signatures to use IProgress<T> + CancellationToken, with cancellation checks between cycles.
• Add internal SynchronousProgress<T> helper and wire GetADReplAccountCommand to use it, with StopProcessing/Dispose managing a CancellationTokenSource.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
Src/DSInternals.Replication/ReplicationProgressHandler.cs	Removes the legacy delegate type.
Src/DSInternals.Replication/ReplicationProgress.cs	New record struct carrying cookie + counts for progress reports.
Src/DSInternals.Replication/DirectoryReplicationClient.cs	Migrates 3 public methods to IProgress<ReplicationProgress> + CancellationToken.
Src/DSInternals.PowerShell/Commands/Replication/GetADReplAccountCommand.cs	Uses SynchronousProgress<T>, adds StopProcessing/Dispose for cancellation, wraps work in try/catch/finally.
Src/DSInternals.PowerShell/Commands/Base/SynchronousProgress.cs	New internal pipeline-thread IProgress<T> helper, with rationale in remarks.
Documentation/CHANGELOG.md	Documents breaking API change under Unreleased → Changed.

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