agent: Don't render usage callouts when not using the Zed provider (#30025)

This PR makes it so we don't render the usage callouts when not using
the Zed provider.

Release Notes:

- Agent Beta: Changed usage callouts to only be displayed when using a
model through the Zed provider.

crates/agent/src/message_editor.rs

@@ -26,7 +26,10 @@ use gpui::{
     Task, TextStyle, WeakEntity, linear_color_stop, linear_gradient, point, pulsating_between,
 };
 use language::{Buffer, Language};
-use language_model::{ConfiguredModel, LanguageModelRequestMessage, MessageContent, RequestUsage};
+use language_model::{
+    ConfiguredModel, LanguageModelRequestMessage, MessageContent, RequestUsage,
+    ZED_CLOUD_PROVIDER_ID,
+};
 use language_model_selector::ToggleModelSelector;
 use multi_buffer;
 use project::Project;
@@ -1071,6 +1074,17 @@ impl MessageEditor {
             return None;
         }
 
+        let is_using_zed_provider = self
+            .thread
+            .read(cx)
+            .configured_model()
+            .map_or(false, |model| {
+                model.provider.id().0 == ZED_CLOUD_PROVIDER_ID
+            });
+        if !is_using_zed_provider {
+            return None;
+        }
+
         let user_store = self.user_store.read(cx);
 
         let ubb_enable = user_store