Forward Rate limits to the UI (#3965)

We currently get information about rate limits in the response headers.
We want to forward them to the clients to have better transparency.
UI/UX plans have been discussed and this information is needed.

codex-rs/core/src/client_common.rs

@@ -1,6 +1,7 @@
 use crate::error::Result;
 use crate::model_family::ModelFamily;
 use crate::openai_tools::OpenAiTool;
+use crate::protocol::RateLimitSnapshotEvent;
 use crate::protocol::TokenUsage;
 use codex_apply_patch::APPLY_PATCH_TOOL_INSTRUCTIONS;
 use codex_protocol::config_types::ReasoningEffort as ReasoningEffortConfig;
@@ -78,6 +79,7 @@ pub enum ResponseEvent {
     WebSearchCallBegin {
         call_id: String,
     },
+    RateLimits(RateLimitSnapshotEvent),
 }
 
 #[derive(Debug, Serialize)]