Remove step-scoped data from extension contributors (#34734)

## What changed

- Remove the step-scoped `ExtensionData` argument from context, turn-input, and tool contributors.
- Pass the host's optional `McpResourceClient` through `ThreadStartInput` so extensions can retain session capabilities explicitly.
- Keep the MCP resource client in skills-owned session state for catalog loading and skill tools.

GitOrigin-RevId: bafa77bcd998aff408d6a396c5fd9ac268c4cce4

codex-rs/core/src/compact_tests.rs

@@ -24,7 +24,6 @@ async fn process_compacted_history_with_test_session(
             &turn_context,
             world_state.as_ref(),
             step_context.mcp.as_ref(),
-            &step_context.extension_data,
         )
         .await;
     let initial_context_injection = InitialContextInjection::BeforeLastUserMessage {