Reuse conversation cache when streaming edits (#30245)

Release Notes:

- Improved latency when the agent applies edits.

crates/language_model/src/fake_provider.rs

@@ -2,6 +2,7 @@ use crate::{
     AuthenticateError, LanguageModel, LanguageModelCompletionError, LanguageModelCompletionEvent,
     LanguageModelId, LanguageModelName, LanguageModelProvider, LanguageModelProviderId,
     LanguageModelProviderName, LanguageModelProviderState, LanguageModelRequest,
+    LanguageModelToolChoice,
 };
 use futures::{FutureExt, StreamExt, channel::mpsc, future::BoxFuture, stream::BoxStream};
 use gpui::{AnyView, App, AsyncApp, Entity, Task, Window};
@@ -152,6 +153,10 @@ impl LanguageModel for FakeLanguageModel {
         false
     }
 
+    fn supports_tool_choice(&self, _choice: LanguageModelToolChoice) -> bool {
+        false
+    }
+
     fn telemetry_id(&self) -> String {
         "fake".to_string()
     }