agent: Show a notice when reaching consecutive tool use limits (#29833)

This PR adds a notice when reaching consecutive tool use limits when
using normal mode.

Here's an example with the limit artificially lowered to 2 consecutive
tool uses:


https://github.com/user-attachments/assets/32da8d38-67de-4d6b-8f24-754d2518e5d4

Release Notes:

- agent: Added a notice when reaching consecutive tool use limits when
using a model in normal mode.

crates/language_model/src/language_model.rs

@@ -66,15 +66,16 @@ pub struct LanguageModelCacheConfiguration {
 
 #[derive(Debug, PartialEq, Clone, Copy, Serialize, Deserialize)]
 #[serde(tag = "status", rename_all = "snake_case")]
-pub enum QueueState {
+pub enum CompletionRequestStatus {
     Queued { position: usize },
     Started,
+    ToolUseLimitReached,
 }
 
 /// A completion event from a language model.
 #[derive(Debug, PartialEq, Clone, Serialize, Deserialize)]
 pub enum LanguageModelCompletionEvent {
-    QueueUpdate(QueueState),
+    QueueUpdate(CompletionRequestStatus),
     Stop(StopReason),
     Text(String),
     Thinking {