Expose event creation timestamp through StreamEvent

[qodo-free-for-open-source-projects]

Description

• Event consumers need access to the creation timestamp when reading from event streams
• All store implementations already have timestamp data available but were not exposing it
• Documentation should reflect the recommended source generator approach for type registration

Deliverables

• StreamEvent field: Add Created DateTime parameter to StreamEvent record struct
• Store implementations: Update all store implementations (KurrentDB, SQL variants, Redis, ElasticSearch, InMemory) to populate the Created field
• Documentation update: Revise serialization docs to emphasize source generator approach and document EVTC001 analyzer

[linear]

EVE-223