Refactor IEventReader to use IAsyncEnumerable for streaming event reads

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

Description

• The current IEventReader interface returns materialized Task<StreamEvent[]> arrays, which is inefficient for large streams as it requires loading all events into memory
• The failIfNotFound parameter creates inconsistent behavior across implementations and complicates the interface contract
• Streaming results with IAsyncEnumerable enables memory-efficient processing of large event streams while maintaining backward compatibility through extension methods

Deliverables

• Interface redesign: Change ReadEvents and ReadEventsBackwards to return IAsyncEnumerable<StreamEvent> without failIfNotFound parameter
• Backward compatibility: Implement extension methods in StoreFunctions that preserve old signatures with failIfNotFound behavior
• Implementation updates: Refactor all event store implementations (KurrentDB, SQL, Redis, Elastic, InMemory, Tiered, Traced) to use async enumerable with yield return
• Tracing support: Add TraceEnumerable method to BaseTracer for proper instrumentation of async enumerable operations

[linear]

EVE-227