Rework snapshotting to allow single request snapshot + events streams

[hjohn]

• Replaces the two-phase snapshot-then-events approach with a unified stream model. A new SourcingStrategy.Snapshot variant on SourcingCondition expresses snapshot intent declaratively; SnapshotCapableEventStorageEngine (a decorator) resolves it by loading the snapshot and prepending a synthetic SnapshotEventMessage to the event stream - giving callers a single, contiguous stream to reduce
• Introduces EntityLifecycleHandler as the primary abstraction replacing SourcingHandler, consolidating initialize, source, and subscribe into one contract. SnapshottingEntityLifecycleHandler replaces both SnapshottingSourcingHandler and StoreBackedSnapshotter, centralising snapshot load/store logic alongside entity evolution
• EventSourcingRepository is simplified to a single EntityLifecycleHandler constructor parameter; the old multi-field wiring (eventStore, entityFactory, entityEvolver, sourcingHandler fields) is gone
• Removes Snapshotter interface and StoreBackedSnapshotter as separate collaborators; removes SnapshottingSourcingHandler; renames SimpleSourcingHandler is replaced by SimpleEntityLifecycleHandler

[sonarqubecloud]

Quality Gate passed

Issues
27 New issues
0 Accepted issues

Measures
0 Security Hotspots
90.8% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud