Distributed queues and cluster events through Mediator extension points

[ejsmith]

Adds queued handlers and cluster notifications using Foundatio #533. The existing Mediator runtime, source generators, and core tests match main exactly. This is an alternative to #149 built through existing extension points.

Developer experience

Configure the infrastructure once:

var foundatio = builder.Services.AddFoundatio();
foundatio.Messaging.UseAws();
foundatio.Jobs.UseRedis();
foundatio.Locking.UseRedis();
builder.Services.AddMediator().AddDistributedQueues();

Add [Queue] to an ordinary handler:

[Queue(TrackProgress = true, Concurrency = 4, MaxAttempts = 3)]
public class ExportReportHandler
{
    public async Task<Result> HandleAsync(ExportReport message,
        IReportService reports, MessageProcessingContext context, CancellationToken ct)
    {
        await reports.ExportAsync(message.ReportId, ct);
        await context.ReportProgressAsync(100, "Report ready", ct);
        return Result.Ok();
    }
}

• Enqueue: mediator.EnqueueAsync(new ExportReport("monthly"), ct) returns Result<QueueReceipt> confirming broker acceptance.
• Validate and track: ordinary middleware runs before enqueue; native Foundatio APIs provide progress and cancellation. [Queue] configures retries/concurrency; [QueueLock] adds resource locking.
• Broadcast: AddDistributedNotifications(o => o.Include<OrderChanged>()), then mediator.PublishAsync(...). Typed subscriptions exclude unrelated local traffic; overlapping selections publish once. No local handler is required.
• Operate and scale: select workers by queue/group, inspect/replay/delete dead letters, and follow jobs/live events in the console and Clean Architecture samples. Processing jobs appear first in the dashboard.

Performance

Median jobs/sec, system .NET 10.0.12 Release, concurrency 64:

Scenario	#149	This PR
In memory	181,195	100,346
In memory, tracked	36,658	34,111
SQS / LocalStack	2,788	2,968
In memory + Redis tracking	10,619	7,600
SQS / LocalStack + Redis tracking	2,702	2,582

This pass improves untracked memory throughput 5–8% with about 5% fewer allocations. Longer tracked-memory runs were level; Redis was 4% slower, with 5% less CPU. #149 remains leaner in memory; LocalStack is not production AWS capacity. Method, layer isolation, latency and raw results.

Additional details

• Rebased on main. One integration package; no distributed changes to Mediator core. Foundatio is pinned to 56a88f0a on #533; publishing waits for those APIs to ship.
• Queues are at least once; cluster broadcasts are best effort. Receipts confirm acceptance, not completed business work.
• Release builds now preserve native dependency configuration; CI rejects unoptimized benchmark assemblies.
• Passed: 756 .NET tests, 23 browser scenarios, console workflow and docs. 7.52M comparison jobs had no missing/duplicate deliveries. A ten-minute 69,354-job run verified queued/running cancellation, forced crash recovery and graceful worker restart, with no pending or failed jobs.