feat: open-source global ProjectionV2 with sync/async event-driven execution

[dgafka]

Why is this change proposed?

ProjectionV2 is currently entirely gated behind an enterprise licence. Users who want globally-tracked projection that follows event store position cannot use it without purchasing a licence. This change makes the core projection capability available in open-source — giving users production-ready globally-tracked projections — while keeping scaling, operational, and deployment features as enterprise value-adds.

This will allow current Ecotone users to migrates from Projection(v1) to ProjectionV2 - which will allow in Ecotone 2.0 for complete removal of old projecting system.

Description of Changes

Open-source features (no licence required)

#[ProjectionV2('in_progress_tickets')]
#[FromStream(Ticket::class)]
class InProgressTicketList
{
    #[EventHandler]
    public function onTicketCreated(TicketCreated $event): void
    {
        // Write to read model
    }

    #[ProjectionInitialization]
    public function init(): void { /* CREATE TABLE ... */ }

    #[ProjectionDelete]
    public function delete(): void { /* DROP TABLE ... */ }

    #[ProjectionReset]
    public function reset(): void { /* DELETE FROM ... */ }
}

Also supported without licence:

• Async event-driven via #[Asynchronous('channel')]
• Multiple #[FromStream] / #[FromAggregateStream] on same projection
• #[ProjectionExecution(eventLoadingBatchSize: 500)]
• #[ProjectionBackfill] (sync only, no asyncChannelName)
• #[ProjectionState] for stateful handlers
• Event emission via EventStreamEmitter
• Gap detection, locking, batch loading

Enterprise-only features (require licence)

// These attributes require enterprise licence:
#[Partitioned]           // Partition-based scaling
#[Streaming('channel')]  // Streaming channel consumption
#[Polling('endpoint')]   // Polling execution mode
#[ProjectionRebuild]     // Rebuild capability
#[ProjectionDeployment(manualKickOff: true, live: false)]  // Blue-green
#[ProjectionBackfill(asyncChannelName: 'backfill')]  // Async backfill

Custom implementations of #[StreamSource], #[StateStorage], #[PartitionProvider] also require enterprise licence.

Use case scenarios

1. Read model projection — A team building a CQRS app needs a projection that maintains a denormalized read model from event-sourced aggregates. With this change, they can use #[ProjectionV2] + #[FromStream] out of the box.

2. Multi-stream aggregation — A dashboard projection consuming events from multiple aggregate streams (e.g., Orders + Payments) works without licence using multiple #[FromStream] attributes.

3. Scaling to production — When the team needs partition-based parallel processing, async rebuild, or blue-green deployment, they upgrade to enterprise.

Feature split diagram

flowchart TD
    PV2["#[ProjectionV2]"] --> OSCheck{Open-source eligible?}
    
    OSCheck -->|Global + sync/async event-driven| OS["Open Source ✓"]
    OSCheck -->|Partitioned / Streaming / Polling| ENT["Enterprise Required"]
    OSCheck -->|ProjectionRebuild / Deployment| ENT
    OSCheck -->|Async backfill| ENT
    OSCheck -->|Custom StreamSource / StateStorage| ENT
    
    OS --> Features["Lifecycle • Multi-stream • Backfill (sync)\nGap detection • Locking • Batch loading\nEvent emission • ProjectionState"]

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