Fix extension turn item emitter test event ordering

[bolinfest]

Why

PR #24813 added extension TurnItemEmitter coverage and introduced a test that records a conversation history item before asserting extension-emitted turn item events.

record_conversation_items() also emits a RawResponseItem event to observers. The test was reading from the same event receiver and expected the next event to be ItemStarted, so the test failed reliably once the setup history item was present.

What Changed

Update passes_turn_fields_and_scoped_turn_item_emitter_to_extension_call to consume and assert the expected setup RawResponseItem before checking the extension ItemStarted, WebSearchBegin, ItemCompleted, and WebSearchEnd events.

This is test-only and does not change extension runtime behavior.

Verification

• cargo nextest run --no-fail-fast -p codex-core tools::handlers::extension_tools::tests::passes_turn_fields_and_scoped_turn_item_emitter_to_extension_call