Add excludeTurns parameter to thread/resume and thread/fork (#19014)

For callers who expect to be paginating the results for the UI, they can
now call thread/resume or thread/fork with excludeturns:true so it will
not fetch any pages of turns, and instead only set up the subscription.
That call can be immediately followed by pagination requests to
thread/turns/list to fetch pages of turns according to the UI's current
interactions.

codex-rs/app-server/src/thread_state.rs

@@ -31,6 +31,7 @@ pub(crate) struct PendingThreadResumeRequest {
     pub(crate) config_snapshot: ThreadConfigSnapshot,
     pub(crate) instruction_sources: Vec<AbsolutePathBuf>,
     pub(crate) thread_summary: codex_app_server_protocol::Thread,
+    pub(crate) include_turns: bool,
 }
 
 // ThreadListenerCommand is used to perform operations in the context of the thread listener, for serialization purposes.