tests: src/streaming_flow_tests.rs tests streaming but there is no streaming API in the contract

[Haroldwonder]

Problem

src/streaming_flow_tests.rs tests multi-step async streaming flows, but the AnchorKitContract has no streaming API. Soroban contracts are synchronous and cannot push updates. The streaming tests appear to simulate a pattern that is not actually implemented in the contract.

Location

src/streaming_flow_tests.rs

Fix

Either implement a streaming-compatible pattern (e.g. polling with transaction state updates) in the contract and document it, or remove the streaming tests and replace them with tests for the actual polling-based state update flow.