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/ext/goal/src/extension.rs

@@ -420,7 +420,6 @@ where
         &self,
         _session_store: &ExtensionData,
         thread_store: &ExtensionData,
-        _step_store: &ExtensionData,
     ) -> Vec<Arc<dyn codex_extension_api::ToolExecutor<codex_extension_api::ToolCall>>> {
         let Some(runtime) = goal_runtime_handle(thread_store) else {
             return Vec::new();