Start separating authentication from connection to collab (#35471)

This pull request should be idempotent, but lays the groundwork for
avoiding to connect to collab in order to interact with AI features
provided by Zed.

Release Notes:

- N/A

---------

Co-authored-by: Marshall Bowers <git@maxdeviant.com>
Co-authored-by: Richard Feldman <oss@rtfeldman.com>

crates/eval/src/instance.rs

@@ -221,7 +221,6 @@ impl ExampleInstance {
         let prompt_store = None;
         let thread_store = ThreadStore::load(
             project.clone(),
-            app_state.cloud_user_store.clone(),
             tools,
             prompt_store,
             app_state.prompt_builder.clone(),